The pennant race is baseball's regular-season lifeblood. And ever since MLB changed its playoff structure to incorporate a winner-take-all Wild Card Game in 2012, those races have regained their old-school feel.

Winning the division is of paramount importance once again, and -- as we saw in the American League West on the final weekend -- the addition of a Wild Card spot simply adds another exciting wrinkle.

The offseason isn't over, and there are still a few dominoes left to fall. But the preliminary readings on those 2016 pennant races are beginning to take shape. With that in mind, here's a breakdown of 2016's most fun races to watch, division by division, starting with the National League East.

6. NL East

Competitive? It should be, but probably only between two clubs
Fun storylines: The Mets' all-world rotation, Bryce Harper's MVP encore, the Harper/Jonathan Papelbon saga in D.C., Jose Fernandez's trade prospects, the Phillies and Braves rebuild
Must-watch players: The entire Mets' rotation, Harper, Giancarlo Stanton, Max Scherzer, Jose Fernandez
Potentially great teams: Mets, Nationals

It says a lot about the state of parity in baseball that the least competitive division -- on paper, at least -- is the NL East, which is still quite competitive at the top. The Mets and Nationals could very well be developing a legitimate rivalry, and both clubs have the pieces in place to make a run in 2016.

But the most fun aspect of the NL East, as currently formed, is that both frontrunners have obvious flaws to go along with their talent. The Mets, probably the favorites after their run to the World Series last October, need offense -- specifically someone to fill the middle-of-the-order void left by Yoenis Cespedes. (That could end up being Cespedes himself.) The Nationals, meanwhile, will be breaking in rookie shortstop Trea Turner, and have some questions at the back end of their rotation and in their outfield.

Both clubs are loaded with talent in certain spots, but clearly lacking in others. And who knows? Maybe if the Marlins stay healthy -- a major "if," given the past couple of seasons -- they end up surprising the baseball world in 2016.

5. AL Central

Competitive? Possibly, if someone challenges the Royals
Fun storylines: Royals look to repeat, Byron Buxton/Miguel Sano take center stage in Minnesota, can Francisco Lindor push the Indians over the top?, are the aging Tigers still a contender?
Must-watch players: Miguel Cabrera, Lorenzo Cain, Miguel Sano, Eric Hosmer, Wade Davis, Francisco Lindor, Corey Kluber, Michael Brantley, Chris Sale, Jose Abreu, Todd Frazier
Potentially great teams: Royals, Indians

The AL Central probably would have finished at the bottom of this list for 2015. And it ranks low again for one main reason: We just don't know if anyone can actually compete with the Royals. Kansas City thoroughly dispatched its four Central competitors last season en route to the World Series, and most of the roster remains intact. That makes the Royals prohibitive favorites in the Central entering Spring Training -- a position they haven't held since, well, ever. (Or at least since 1994 when the Central division came into existence.)

But there's plenty of competition, too. The Twins burst onto the scene last season, and have the young core in place to be very good for several years. The Indians could be ready to take the next step -- although they've appeared ready to do that for a few years now. And the Tigers are something of a mystery, seemingly having attempted to skip their rebuild altogether with the Jordan Zimmermann signing.

Still, at this point the Central is Kansas City's to lose.

4. AL East

Competitive? Yes, it's completely up for grabs
Fun storylines: Rivalries everywhere, David Price in Boston (facing two former teams in his division), David Ortiz's farewell tour, the Jays' juggernaut offense, A-Rod (as always), the Yankees' three-headed bullpen monster
Must-watch players: Josh Donaldson, David Price, Jose Bautista, Manny Machado, Chris Archer, Alex Rodriguez, David Ortiz, Adam Jones, Troy Tulowitzki, Craig Kimbrel, all three Yankees "closers"
Potentially great teams: Probably none

Now we're getting into the really fun divisions. The AL East's case for being the sport's most entertaining bunch rests with the fact that it's entirely unpredictable. If any of the five teams were to win the East in 2016, it wouldn't register as even a minor surprise. There's also no shortage of star power in the East, with reigning MVP Donaldson and Cy Young runner-up David Price leading a group of bona fide superstars (see above).

Plus, these teams clearly don't like each other -- and the contempt stretches well beyond just the Yankees-Red Sox rivalry. Over the past six seasons, all five teams have won the AL East at least once. The only factor that brings the East down in this list is that right now none of these teams could be considered a title favorite.

3. AL West

Competitive? Very
Fun storylines: The battle for the Lone Star State, Carlos Correa's rise to stardom, Mike Trout being Mike Trout, the Mariners' overhaul, Yu Darvish's Tommy John comeback
Must-watch players: Trout, Dallas Keuchel, Carlos Correa, Adrian Beltre, Jose Altuve, Sonny Gray, Cole Hamels, Darvish, Felix Hernandez
Potentially great teams: Astros, Rangers

Allow me to present Exhibit A for why we know nothing when it comes to making baseball predictions: the 2015 AL West. Just about everybody had the Rangers and Astros pegged as bottom-dwellers a year ago, while the three other clubs were expected to compete for a division crown. As it turned out, the Rangers and Astros not only made the playoffs, but came within an ALDS Game 5 win apiece from squaring off in the ALCS.

There is no reason to think either team should experience a drop-off in 2016. If anything, they should get better. Houston's middle-infield duo of Altuve and Correa is probably the best in the sport, and Keuchel is the AL's truest ace right now. Plus, the Astros fixed their only semi-weak spot by adding closer Ken Giles. Texas, meanwhile, is in a similar position, with its core returning and Joey Gallo potentially poised to break through. Plus, if Darvish reverts back to his old self upon his return, the Rangers will own the game's premier 1-2 rotation punch with him and Hamels.

And the crazy thing is, even with all the talent in the Lone Star State, you can't consider this a two-horse race. The Angels were a 98-win team just two seasons ago, and no one was more active early this offseason than the Mariners.

2. NL West

Competitive? At the top, very much so
Fun storylines: The new-look D-backs, Zack Greinke vs. his former team, the even-year Giants, Clayton Kershaw's dominance, the newest chapter in the Giants-Dodgers rivalry, Nolan Arenado's wizardry
Must-watch players: Kershaw, Greinke, Paul Goldschmidt, Madison Bumgarner, Arenado, Buster Posey, A.J. Pollock
Potentially great teams: Dodgers, Giants, D-backs

No division saw more turnover than the National League West this past offseason. The Giants added World Series hero Johnny Cueto to their rotation, along with Jeff Samardzija -- both of whom should fit very nicely in AT&T Park. Arizona, meanwhile, traded for Shelby Miller after swooping in to sign Greinke, a devastating blow to the division-rival Dodgers.

And yet, even after all that, the Dodgers might still be the favorites in the NL West. They're certainly the most complete team, for whatever that's worth. Their rotation may not be as top-heavy as it was last season, but it's deeper than anyone else's, and they have fewer holes to fill in their lineup -- although they have less star power, too.

That said, L.A. suffered a significant loss in Greinke, and there were simply so many moving pieces within the division that there's no clear frontrunner right now.

1. NL Central

Competitive? It's a three-horse race -- and they're all thoroughbreds
Fun storylines: Cubs-Cardinals rivalry hits new heights, Jason Heyward and John Lackey ditch St. Louis for Chicago, Wild Card Pirates (again)?, Kris Bryant's sophomore encore, Adam Wainwright's return
Must-watch players: Andrew McCutchen, Joey Votto, Jake Arrieta, Bryant, Anthony Rizzo, Gerrit Cole, Matt Carpenter, Yadier Molina, Heyward
Potentially great teams: Cubs, Cardinals, Pirates

The Cardinals, Pirates and Cubs finished 1-2-3 in the Central in 2015 -- and in the Major Leagues as a whole. Since MLB went to its six-division format in 1994, three teams from the same division had never finished in the top-six overall, let alone first, second and third. Put simply: The 2015 NL Central was the best division of all-time.

Since the end of last season, the plot has only thickened. In a fierce bidding war, Chicago managed to pry Heyward away from the Cardinals, filling their center-field void. The Cubs may have finished in third place last year, but they eliminated the Pirates and Cardinals anyway, meaning those two clubs will be out for revenge. (Plus, in case you hadn't heard, the Cardinals and Cubs don't exactly like each other, anyway.)

All three of these teams would be considered favorites in just about any other division in baseball. Unfortunately for them -- and fortunately for us as viewers -- they all play in the same division. The Cubs probably have the early edge, given their additions and the Cardinals' subtractions. But even then, it's too close to call.

Chances are it'll be a summer-long dogfight. And with these teams set to play each other a total of 57 times, the entertainment value will be through the roof. In the NL Central, rivalry-fueled pennant-race baseball is truly alive and well.

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AJ Cassavell is a reporter for MLB.com. Follow him on Twitter @ajcassavell.

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