Selecting the greatest defenses of the Super Bowl era is a little like choosing the best-looking vintage automobiles. There is an "eye of the beholder" factor. But there are other, more black and white factors when discerning great defenses, like statistics, schematic advantages, championships and player legacies.

The dominant performance of the Seahawks defense in Super Bowl XLVIII has re-opened the discussion, and the perspective of time will give us a better feel for the historical significance of their accomplishments. In the moment, though, it is difficult to refute that the Seahawks belong in the conversation.

With help from many who played and coached for and against these units, here are my top 10 defenses of the modern NFL. Some of the great defenses dominated over a period of years, in which case only the year that was deemed the best was considered.

1. 1985 Bears

Never in the history of football has a defense intimidated quarterbacks any better. Playing with passion, ruthlessness and cunning, the 1985 Bears forced seven quarterback substitutions over the course of the season.

This may have been the best blitzing team of all time. The front seven was loaded with phenomenal pass-rushing talent, including Hall of Famers Richard Dent, Dan Hampton and Mike Singletary. Also in the mix were Steve McMichael, who ranks third all-time among defensive tackles in sacks, and outside linebacker Wilber Marshall, who some think was the most talented player on the unit. The defense featured nine players who would at some point play in a Pro Bowl.

What's more, the Bears had a cutting-edge scheme: Buddy Ryan's 46. "Buddy did a great job of coaching them," said Mike Ditka, head coach of the '85 Bears. "That was a big part of it. He was doing something nobody else was doing. At that time, people didn't understand our system. You wanted to keep people in to block it, and that was the worst thing you could do because you couldn't have enough people to block it and you wouldn't know which ones were coming."

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Otis Wilson and Mike Singletary helped power the legendary '85 Bears defense to a Super Bowl. (Getty)

What separated the '85 Bears from the rest is they could beat offenses with overwhelming athleticism as well as with scheme. "I think the Bears were the best because they had a combination of talent and confusion that got you," said Cowboys quarterbacks coach Wade Wilson, who played against the Bears as a member of the Vikings.

As the season went on, this monster kept getting meaner, wilder and more oppressive. They shut out their first two playoff opponents; then, in a lopsided Super Bowl victory, they had seven sacks, held the Patriots to seven rushing yards and scored nine points. "I've never seen a defense like that in terms of smothering people, not even letting them move the ball, let alone score," said former Colts and Bucs coach Tony Dungy.

The '85 Bears are thought of as somewhat of a one-hit wonder because they never won another Super Bowl, but their defense actually was superior over a period of time. In 1984, they set the record for most sacks in a season with 72. In 1986, the Bears allowed 11 fewer points than they did in 1985, and were statistically much better than the defense of the Super Bowl champion Giants. In 1987, the Bears sacked quarterbacks 70 times.

Wilson once had to come off the bench in a game against the Bears when he was the Vikings' backup, and he was not very enthusiastic about the opportunity. "I remember telling Archie [Manning], 'You're OK, come on, champ, get up, come on.'" Wilson once told me. "But after the 11th sack, he wasn't getting up. It wasn't a great feeling having to go in there against those guys at that point."

2. 1976 Steelers

"Those old Steelers defenses were the greatest," said John Madden, whose Raiders beat the Steelers in the conference championship game that year. "You just look at those guys that played in that defense. You knew they were great. The guy who used to give us the most trouble was Ernie Holmes, and he wouldn't even get a mention if you talked about great Steeler defenses. We couldn't get Ernie blocked."

Holmes was not even one of eight Steelers defenders chosen for the Pro Bowl that year. Four of his teammates from this defense -- Mel Blount, Mean Joe Greene, Jack Ham and Jack Lambert -- are in the Pro Football Hall of Fame. Many think L.C. Greenwood should join them. Lambert was the NFL's defensive player of the year in 1976.

Given the Steelers' talent, opponents had no answers for the "Stunt 4-3" defense devised by assistants George Perles and Bud Carson. The concentration of great players on that team was overwhelming, which is why some like Holmes could be overlooked. "That's not going to happen anymore because in this salary-cap era you couldn't have Jack Ham, Jack Lambert, Andy Russell, Mike Wagner, Mel Blount, Glen Edwards and all that front four," said Dungy, who joined the Steelers as a defensive back the following season. "You just couldn't pay them all. That kind of defense isn't going to happen."

You could argue the 1974 Steelers were better than the1976 Steelers because the '76 team failed to win a Super Bowl. The '74 defense was best in the league in yards allowed, takeaways, sacks and opponent passer rating. The '76 team was worse in all four categories, but better in the category that counts most -- points allowed. The 1976 Steelers gave up 51 fewer points than the '74 team, and allowed only 28 points over their last nine games. The 76 Steelers shut out five teams, an NFL record.

This defense excelled over a long period of time. Between 1972 and 1979, the Steel Curtain never fell out of the top 10 in total defense, and ranked in the top three six times.

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Ray Lewis and the Ravens defense allowed only 970 rushing yards all season in 2000. (Getty)

3. 2000 Ravens

Arguably, this was the best run defense ever. The Ravens held opponents to 2.69 yards per rush -- the best since the 1951 Giants. They gave up only 970 rushing yards and never allowed a 100-yard rusher despite facing the likes of Emmitt Smith, Curtis Martin, Jerome Bettis, Eddie George, Tiki Barber, Fred Taylor and Corey Dillon. Howard Mudd, who was a part of the league as a player or assistant coach for 44 years, compared the 2000 Ravens to the Steel Curtain in terms of their ability to stop the run.

"They were very, very good against the run," said Rams coach and Jeff Fisher, who coached three games against the 2000 Ravens when he was with the Titans and knows a little about great defenses, given his Super Bowl ring from the '85 Bears. "Ray Lewis was the ultimate run stopper. The playoff game we lost to them, Ray scored a touchdown [on a 50-yard interception return]. Our defense held their offense to 134 yards of offense and we lost 24-10."

This defense was known for its physicality. The Ravens were not just about muscle, though. "Their aptitude for the opponent made them special," said Bengals coach Marvin Lewis, who was the defensive coordinator for that team. "Obviously, they were great, great players. But they were so in tune to what the opponent did tendency wise, personnel wise and formation wise, and they beat people to the spots. I would run a play in practice on a Thursday and Goose [Tony Siragusa] or somebody would stand up and say, 'Wait a minute, you can't do that. They don't run it that way.' As a group they were very smart players."

The Ravens also had the advantage of a stacked coaching staff with four head coaches on the defensive side of the ball in Marvin Lewis, Jack Del Rio, Mike Smith and Rex Ryan. "Our coaches did a great job of taking it from our lab to the players' lab and getting them in tune with it," Lewis said.

As many of the great defenses have done, the 2000 Ravens peaked at the right time. In the postseason they allowed an average of four offensive points per game, and they held the Giants without an offensive touchdown in the Super Bowl. They allowed only 165 points -- the fewest by any team in a 16-game season -- and the defense had little help from an offense that ranked 16th in the league

4. 2013 Seahawks

In the Super Bowl, the Seahawks absolutely crushed the Broncos offense that scored the most points in regular-season history. But that was just the finishing touch. They allowed 14.4 points per game in a season when the league average was 23.4. They limited opponents to 5.82 yards per pass attempt in a year when the worst team, the Bucs, averaged 6.19 yards per pass. They were best in the league in points allowed, yards allowed, takeaways and opponent passer rating.

"Not only did they perform at the Super Bowl, but they performed all year against a variety of different offenses and good quarterbacks, at home and on the road," Fisher said. "For them to line up and play the 49ers the way they did, with the versatility of that offense, the commitment of the run game and the mobility of the offense, that was impressive."

If the Seahawks defense had played a decade ago the way its did this year, it would not have been as impressive. But the advances in offensive football gave the 2013 Seahawks defense unquestioned credibility. "What they did stands out because of the way rule changes have affected offense," said Ravens general manager Ozzie Newsome, who played against the Steel Curtain and the Bears in the mid-'80s and put together the 2000 Ravens. "More scoring, the rules favor that. Back in the day, corners could absolutely beat guys up."

The challenges the Seahawks overcame are part of what defined them. "I think it's one of the best defenses ever, but it's hard to compare," said former Cowboys personnel executive Gil Brandt, who has been associated with the NFL since 1960. "The '85 Bears, they played against 'Red' and 'Brown.' There weren't a lot of formations and motion and all of that. Football was simpler than it is now. It was man on man, so to speak. With all of the offensive looks now, it's harder. But I think if this defense had played in 1985 or any year, it would have been pretty good."

The argument also could be made that defensive football has regressed in recent years. New rules limiting offseason preparation and in-season practices have led to a poor tackling epidemic. But the Seahawks went against the trend. "The thing that is outstanding about Seattle is they are very, very good tacklers," Hall of Fame coach Bill Parcells said. "The majority of them are good tacklers. They particularly tackle well in the secondary. That is a place where poor tackling shows up. Not there."

Regardless of where their overall defense ranks, the Seahawks might be able to lay claim to the title of best secondary ever. Hall of Fame quarterback Warren Moon, who serves as the color analyst for Seahawks games on the radio, said he has not seen a better secondary in his 30-year association with the NFL. Some may prefer the 1994 49ers (Deion Sanders, Eric Davis, Merton Hanks, Tim McDonald). Others may pick the 1984 49ers (Ronnie Lott, Eric Wright, Carlton Williamson, Dwight Hicks). Still others will like the1984 Raiders (Mike Haynes, Lester Hayes, Vann McElroy, Mike Davis). But with Richard Sherman, Earl Thomas and Kam Chancellor all being voted All-Pro, the 2013 Seahawks secondary was as effective as any.

The Seahawks secondary plays differently than many of the other great secondaries and most other current ones. These DBs try to interfere with the route running of receivers, both at the line and beyond. "That secondary is well put together, and the cornerbacks get away with holding," Lewis said, echoing a common refrain. "They didn't hold in the Super Bowl, but they did it all year long. They play the game very aggressively."

The Seahawks may be on the borderline of legal coverage. But they are aware of what they are doing. "They know they will be penalized some because of how they play, but the number of penalties they get are worth it when you compare them to the number of plays they make," Moon said. "They push the rules to the limit to their benefit."

Moon rates the Seahawks overall defense with the 1985 Bears and the 2000 Ravens as the best he ever has seen. "With all three, their physicalness and intensity stand out," Moon said. "They never let up the whole game. A lot of that had to do with special players like Ray Lewis with the Ravens, Mike Singletary with the Bears and Earl Thomas and Kam Chancellor with the Seahawks."

What we can be sure of is this is one of the best collections of big, athletic, skilled players in history. The Seahawks are pretty special in that regard. But in order to be remembered by history like the Steel Curtain and the '85 Bears, the Seahawks D will need to be sustainable. Since it's such a young defense, we have no idea if there is even a single Hall of Fame player on the unit. "I'm not ready to put Seattle with that group yet," Dungy said of the Steelers of the mid-'70s. "You have to see it develop over the course of a couple years and see it over a period of time."

In this era, continuity is difficult. The Seahawks 2014 defense is likely to be without some mainstays from the 2013 defense. Defensive lineman Red Bryant has been cut. Defensive end Chris Clemons could be. Among the significant players whose contracts expire next week are defensive end Michael Bennett, cornerback Brandon Browner, defensive tackle Tony McDaniel and cornerback Walter Thurmond.

The Seahawks defense could be better positioned to overcome personnel losses than most defenses, however. They are so well coached by Pete Carroll, and as a result are one of the most fundamentally sound defenses in the league. Their system appears to be at least as significant as the players who execute it. They have better depth than most, and a willingness to use it.

General manager John Schneider and his staff have excelled at finding players who fit the parameters of Carroll's defense, and Carroll and his staff has excelled at developing players and defining roles that get the most out of individuals. Super Bowl MVP Malcolm Smith was a seventh-round pick. Sherman and Chancellor were fifth-round picks. No one can assume these players would have excelled in other defenses.

Compared to the other defenses in their class, the Seahawks defense was not star-studded. They had only three players voted to the Pro Bowl. Seven of the nine other top-10 teams had more.

"Coaching has a ton to do with who this defense is," Moon said. "A lot of it is the combination of their size and athleticism and intensity. But then you look at how they have used the talent. They take an inside player like Red Bryant and make him a 325-pound end. Not many people would do that. … You look at how Pete makes this team practice. I've never seen a team go at each other during the regular season like this. They go really hard, so that by the time the game gets here it's just a formality. These players have been conditioned this way since they got to Seattle."

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Tackle Warren Sapp and the defense carried the 2002 Buccaneers to a Super Bowl championship. (Getty)

5. 2002 Buccaneers

Dungy built this defense and watched it get progressively better until it peaked the year after the Bucs fired him. Warren Sapp and Derrick Brooks already are Hall of Famers. John Lynch was a finalist this year. Simeon Rice and Ronde Barber are sure to at least be in the Hall of Fame discussion at some point soon. Oh, and Dungy was a finalist this year as well.

This defense should not be overlooked in discussions of the great ones. Including the postseason, they held 11 opponents to 10 points or fewer. Opponents averaged 12.2 points per game against them in a season when the league average was 21.7. And they held opposing passers to a 48.4 rating in a year when the next best defense held opposing passers to a rating of 68.7.

The Bucs defense was consistent throughout the year, but was at its best in the Super Bowl. Against the Raiders and the No. 1 offensive in the NFL, the Bucs had five interceptions and three defensive scores.

"I don't know how you play much better defense than that," said Falcons president Rich McKay, who was the general manager of the Bucs in 2002. "It was a balanced defense. They had dominant players at all three levels. They could play the run and the pass even in a Cover-2 scheme. They could rush the passer with four men, and then benefit from having seven in coverage."

6. 1969 Vikings

The legendary Purple People Eaters led the league in defense three times, but this probably was their finest season, as they allowed only 9.5 points per game-- the second-lowest average of the Super Bowl era. They also held opponents to the fewest rushing yards ever in a 14-game season. Quarterbacks had a 42.1 passer rating against this defense, the best in the NFL.

All four defensive line starters -- Carl Eller, Gary Larsen, Alan Page and Jim Marshall -- went to the Pro Bowl in 1969. Ditka rates the Vikings line of this era as "probably the best I played against."

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The 1966 Packers defense featured six Hall of Famers and won the NFL's first Super Bowl. (Getty)

7. 1966 Packers

The talent on this team was overwhelming, as the first Super Bowl team featured six future Hall of Famers -- Willie Davis, Henry Jordan, Ray Nitschke, Dave Robinson, Willie Wood and Herb Adderley. "They were well coached, sound in everything they did," Ditka said. "But they had a lot of great players. They didn't have to blitz a lot. They just beat you man to man. That's the best way to play defense."

The 1966 Pack held opponents to a 41.5 passer rating when the league average was 63.7.

The 1962 Packers defense probably was even better, but they didn't qualify for these rankings because they came in the pre-Super Bowl era. The Packers played sublime defense over a long stretch in the Lombardi years.

8. 2008 Steelers

This may be the most underrated of all the great defenses. It's underrated in part because Troy Polamalu and James Harrison were the only two real difference-makers. But the scheme run by Dick LeBeau was the star for the Steelers.

They held opponents to an average of 13.9 points per game in a year when the scoring average was 22. Brandt said in that context, the 2008 Steelers were more impressive than the Steel Curtain Steelers. "You have to give the credit to LeBeau in that he came up with a great scheme," Brandt said. The Steelers also held opponents to an average of 3.9 yards per play.

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Bobby Bell and the Chiefs boasted the best defense in AFL history in 1969. (Getty)

9. 1969 Chiefs

This clearly was the best defense in AFL history, but it was not the best defense statistically from the 1969 season, as the Vikings were better. It's a little difficult to compare because the defenses were playing against different offenses. The Chiefs prevailed in the Super Bowl, so that counts for something.

The "stack defense" used by Hank Stram put linebackers directly in back of linemen and gave offenses fits. What stands out most about this defense is it featured five future Hall of Famers in Buck Buchanan, Curley Culp, Bobby Bell, Willie Lanier and Emmitt Thomas. And Johnny Robinson could join them one day.

10. 1973 Dolphins

The undefeated 1972 Dolphins get all the attention, but the 1973 Dolphins played better defense, allowing 21 fewer points against a tougher schedule of opponents. The 150 points allowed in a 14-game season set a record at the time. Even Don Shula has said he believes the '73 Dolphins defense was superior.

They called it the "No Name Defense," and Nick Buoniconti is the only Hall of Famer from the team. But this team had four All-Pros: defensive player of the year Dick Anderson and fellow safety Jake Scott, defensive end Bill Stanfill (18.5 unofficial sacks) and nose tackle Manny Fernandez.