Easy. The Atlanta Braves.
The Braves, you ask?
Talk all you want about the Nationals and the Orioles, and even the unbelievable Oakland Athletics.
What the Braves have done this season is just as significant, and for the most part, it hasn't received the attention it deserves.
Atlanta will be out to nail down a playoff berth this weekend at Philadelphia's Citizens Bank Park, and don't blame the Braves if there's a bit of revenge on their minds.
It was almost a year ago when the Phillies, en route to their fifth consecutive National League East title, completed a three-game season-ending sweep with a stunning 13-inning, 4-3 victory that sent the Braves home for the winter. St. Louis won the NL Wild Card and eventually the World Series.
With less than a month to go in the 2011 season, the Braves held an 8 1/2-game lead for the Wild Card. They were on cruise control.
Then came September. They lost 18 of 26 games, including five in a row to end the season, setting the stage for one of the most unpredictable, exciting final days of the year.
They joined the Boston Red Sox, whose epic collapse tore the storied franchise apart at the seams.
Unlike the Red Sox, the Braves have adroitly, without wholesale changes, picked up the pieces and rebuilt their fortunes.
Granted, they've been the second-best team in the NL East all season, but I believe that they have rebounded so soundly from 2011 it is an enormous achievement. It's been mostly under the radar this year.
History tells us when teams suffer such a devastating collapse, they usually stagger the next season. The 2012 Red Sox are a fitting example.
The Braves trail the Nationals in the division by 5 1/2 games, but Atlanta has a commanding lead as the No. 1 Wild Card under the postseason's new format of two Wild Cards in each league.
If the postseason were to open today, the Braves would play the Cardinals at Turner Field in MLB's version of Russian roulette, a one-game sudden-death playoff on Oct. 5.
If successful, the Braves would remain home and begin the NL Division Series two days later against the Nationals, who own the best record in baseball.
While the Red Sox replaced manager Terry Francona, who won two World Series championships in Boston, with Bobby Valentine, and general manager Theo Epstein went to the Cubs, the Braves held steady to the course that at one point helped them win a record 14 consecutive division titles.
Give team president John Schuerholz, who was the most successful general manager in baseball history, and his successor, Frank Wren, credit.
What happened to the Braves last September is not easy to overcome. Management often pushes the panic button, convinced wholesale changes are necessary.
Wren was convinced that, except for some minor tweaking, the Braves had the pieces in place to contend.
No one expected the Phillies to have such a down year, and the Nationals were an even bigger surprise. The Braves and Marlins were seen as most the clubs most likely to challenge the Phils for the division title.
With likely future Hall of Famer Chipper Jones on his farewell tour and young pitcher Kris Medlen having a phenomenal season, there's reason to believe the Braves can go deep into the postseason.
The emergence of Jason Heyward and a full season in Atlanta for center fielder Michael Bourn has helped put last September in the rearview mirror.
Plus, after legendary manager Bobby Cox retired following the 2010 season, there was a different look in the dugout: Fredi Gonzalez.
I believe it took most of 2011 for the veteran players to feel comfortable with their new skipper. He wasn't Cox.
"It takes time and effort to get over what happened last September," said Gonzalez. "I would have traded any month we had last season for September. The majority of the teams have one bad month or a couple bad weeks, but ours was September."
And St. Louis got hot.
Gonzalez felt it was good to talk about what happened last September during Spring Training, then try to forget about it and move forward.
Jones told MLB.com's Terence Moore that chatter about the collapse never existed among the players.
"And it never will," Jones said. "Absolutely, the quickest way for it to come to the forefront of everybody's mind is to bring it up -- to talk about it. If you do talk about it, you start to tighten the noose yourself, and that's not what you want to do.
"What I try to give off is just a relaxed attitude," he added. "It's like, 'You know what, guys? We're not going to worry about yesterday. We're not going to worry about tomorrow. We're not going to worry about last year. We're going to focus on today's game. We're going to go out and play it as well as we can and let the chips fall where they may.'
"To be honest with you, when the baseball gods decide to go against you, there really is nothing you can do about it."
Medlen gives the Braves one of the deepest rotations in the league, joining right-handers Tim Hudson and Tommy Hanson and lefties Paul Maholm and Mike Minor. Relievers Eric O'Flaherty, Jonny Venters and closer Craig Kimbrel anchor the bullpen. No team in MLB has a better record when leading after six innings.
The Braves' success this season cannot be overstated.
Gonzalez told them not to look back, and obviously they've followed his advice.
Hal Bodley is the senior correspondent for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.