Baseball has clearly become a game defined by specialization. 

Gone are the days when starters pitched 10 complete games in a season. Managers now typically only ask six innings of their starting pitchers as their general managers have most often times tried to find enough power arms with a devastating second pitch to take them through the last third of the game.

And we have seen what teams with dominant bullpens can accomplish. The Kansas City Royals have gone to two straight World Series, winning it all last year, based mainly on the strength of their bullpen, not their starting rotation. And we've seen that, in today's MLB, you cannot have success without a strong bullpen.

However, while starters aren't required to go the distance all that often, having a dominant starting rotation is still the surest way to make the postseason, and advance in the playoffs once you get there. The 162-game season is a marathon, and having a strong, deep, collection of starting pitchers is vital to success.

Below are the five teams with the best rotations in baseball, heading into the 2016 season. And it's not surprise that, according to most experts, all five teams have playoff aspirations.

We'll start with the fifth-best rotation and work our way to the top.

5. Cleveland Indians

From top to bottom, the Cleveland Indians have the most swing-and-miss arms in baseball. Former Cy Young Award winner Corey Kluber and Carlos Carrasco make a ridiculous one-two punch at the top of the rotation, with Danny Salazar a well above average number-three. Trevor Bauer has incredible stuff, but walks far too many hitters. If he can ever figure out how to put the ball over the plate consistently, the Indians could suddenly have themselves another ace.

The reason these five starters are ranked number-five here is that the results on the field haven't been too terrific just yet. Their starters ERA of 3.94 was 10th best in baseball last year, largely because of all the dingers Cleveland starters gave up last year, 1.13 per nine innings among the rotation, 20th in baseball. And their home run per fly ball rate of 12.6% was 21st in the Majors.

Nevertheless, that's a metric that is not necessarily predictive and could normalize this year. If it does, the Indians could end up with the best staff in baseball.

4. Washington Nationals

Going into last year, many thought the Nationals rotation could be one for the ages. With Max Scherzer, Jordan Zimmermann, Stephen Strasburg, Gio Gonzalez and Doug Fister lined up, many were comparing it to the ridiculously good 2011 Phillies rotation that featured Roy Halladay, Cliff Lee, Cole Hamels and Roy Oswalt. But it didn't exactly turn out that way.

Their rotation ERA of 3.70 was still among the 10 best in baseball, seventh overall. But it wasn't historic, which was the expectation. Now Zimmermann is gone, replaced by Joe Ross in the rotation, a decent replacement.

The key to the rotation will be Strasburg. A few weeks ago, Adam Wainwright has begun. And yes, he only made four starts last season due to an injury, but it was not an injury to his arm, shoulder, elbow or anything connected to the throwing of a baseball. Instead, it was an Achilles tear that he recovered from well enough to make it back before the end of the season and put up a 1.44 ERA and 2.05 FIP in 25 innings.

The reason the Cardinals aren't a bit higher is because they don't have the strikeout arms the two teams ahead of them do. But from top to bottom, there isn't an easy day for opposing batters.

Jaime Garcia is one of the most underrated left-handers in the game, Michael Wacha has the stuff to be dominant, although he doesn't have the strikeout stuff he used to. In his rookie season of 2013, he K'd 9.05 batters per nine, but that number has dropped to 7.91 in 2014 and 7.59 last year. Still, that'll get the job done. 

Mike Leake replaces the departed John Lackey (more on him in a moment) and provides solid, if unspectacular, results. The true wild card is Carlos Martinez, who burst onto the scene last year in 174 2/3 innings, putting up a 3.04 ERA and fWAR of 3.4. He has the best pure strikeout stuff on the staff, and at 24 years old could turn out to be the best pitcher on this team.

2. Chicago Cubs

While the Cardinals may have more depth in their starting rotation, the Cubs have a more dominant top three. No one was better than NL Cy Young Award winner Jake Arrieta last year. Of course, there is the red flag I raised in a previous piece about his drastic innings jump last year, he still should be an ace-level starter for Chicago in 2016. Jon Lester got overshadowed a bit by Arrieta last year but still struck out 9.09 batters per nine and was a five-win pitcher for Chicago. 

The Cubs signed Lackey as a free agent, stealing him away from their division rivals, the Cardinals. So, in one move, they strengthened themselves and weakened their top rival. It will be hard for Lackey to repeat his 2.77 ERA and 3.6 fWAR season from a year ago, but if he doesn't, it makes him one of the best number-three starters in the game. 

And while Kyle Hendricks isn't a sexy arm in the number-four slot, he did make 32 starts, put up a 3.36 FIP that indicates he deserved better than his 3.95 ERA. He struck out 8.35 batters per nine and had an fWAR of 3.4. And you can do a lot worse than Jason Hammel and his 2.4 fWAR and 9.07 K/9 in the number-five spot.

1. New York Mets

Simply put, this has a chance to be a historic rotation.

Matt Harvey, fully recovered from Tommy John surgery, will get the Opening Day start, and should be at full strength for a full season since undergoing that surgery. He was plenty good last year when he had a 2.71 ERA and struck out 8.94 batters per nine. Jacob deGrom emerged as a true ace as well, striking out a ridiculous 9.66 batters per nine, with velocity no one thought he'd be able to have when he was in the minors.

But the guy who could end up being the team's best pitcher long-term is the guy they acquired from the Blue Jays for R.A. Dickey. Noah Syndergaard, a.k.a. "Thor," made 24 starts last year and struck out 9.96 batters per nine while walking just 1.86. The scary thing is he could be even better this year. Steven Matz is an injury prone arm who has never put up a lot of innings, but is a terrific left-handed change of pace that can also pile up the strikeouts. 

And while Bartolo Colon will continue to man the number-five spot in the rotation for a while, the team is anxiously awaiting the return of Zack Wheeler, who should be back from injury by mid-season.

A word of caution, however. All four of their top starters pitched more innings last year than ever before, and there is worry about a hangover. I doubt that will happen, but it's a possibility. 

Still, it's easy to see why just about everyone in baseball believes the New York Mets possess the best starting rotation in baseball, and that's unlikely to change anytime soon.