So far, sabermetrically speaking, the Cardinals are the best team in baseball. Their offensive wins above replacement level far outpaces even the Yankees, 11.3 to 8.5. Although both teams are in 2nd place in their respective divisions, so far this year they seem to be the powerhouses of MLB. The Reds come in 3rd in offensive WAR, not too far behind the Yanks. The Rays (the other first place team) are tied with the Royals (!)...
Looking at weighted on base average, the Cards and Yankees are still on top, and the Reds are close. The Rays fall to the middle of the pack in offense. However, the 1st place Rays are also first in the majors in defensive value. The Padres, Cardinals (tied) and Yankees are 6th and 7th in defense, so perhaps the Cardinals have not been as bad as the perception has been to start the season (Reds and Brewers are 10th and 11th in defense).
The biggest surprise of the season, the Cleveland Indians, are 6th in the majors in offense (wOBA-speaking), top 10 in ERA, and 11th in FIP, and middle of the pack in fielding. Their relief corps have been a bit better than their starters, stabilizing their gameplan. To compare, the Cards are middle of the pack in relief, but so far they have had great success with their starters. Overall the Cardinals are 7th in FIP and 10th in ERA. Interestingly, the team's ERA and FIP are nearly identical (3.54 and 3.56).
A question that may be interesting to ask about the Indians, is are they getting lucky? Pitching-wise, teams have only had a .275 BABIP against them. The lowest BABIP by a staff is the Rays', so their pitching success has probably been a bit of an illusion. But the Indians should be able to somewhat continue that success. offensively, the Indians' BABIP is just a tad over .300, so they haven't been especially lucky there either. The Cardinals (and Cubs), however, have both been really lucky offensively with BABIPs over .325. The Yankees have been actually pretty unlucky, despite the offensive rates they have accomplished.
To switch gears, I'm not really sure how the Tigers are 22-18. They are in the middle of the pack in pitching, offense, and fielding. Chalk it up to being in the AL Central, who have only had one dominant team. The Angels have been off to a great start, but also due to being in a weak division. Their fielding is superb, and top 10 in offense. Their primary area of weakness is their bullpen, which I'm sure has caused their fanbase some pause. Their bullpen ERA is passable, but not impressive. Their FIP is pretty bad though, so going forward there may be some nail biting. To put it bluntly, the Angels bullpen have been getting pretty lucky. But good enough for first place in the AL West.
To probably no one's surprise, the Phillies have been the team to beat so far. While their offense has only been adequate, they have the best pitching staff in the majors. While their bullpen has been really lucky, I don't know that it will come close to offsetting the production of their devastating starting pitching (rocking a 2.39 FIP right now!!). One area of concern going forward for the Phillies is their defense, which is not all that great. But who could challenge the Phillies in the NL East? Turns out the Marlins and Braves are pretty damn good too.
The Marlins have an impressively good fielding team so far. They are top 10 in pitching, but with a .270 BABIP against, so likely they are not quite this good. However, their offense is more middle of the pack, so they will probably drop off before too long. But who knows... The Braves are worse at defense, but have been more unlucky by BABIP. So they have more room for improvement and could swap places with the Marlins offensively, going forward. The spot where the Braves could match up well with the Phillies is in pitching. They have the 2nd best pitching staff in the majors, but have a far superior bullpen to the Phillies (their starters are 4th in MLB). The Braves weakness so far has been in fielding though, so this could hurt their pitching.
So what of the Brewers? Their pitching has been quite nice so far, and that has been without their ace for most of the season. So far in 2 starts, Greinke is 1-1 and has the weird stats of 5.40 ERA and a 1.56 FIP. This is of course a small sample size distortion. But I think his 13.5 K:9 and .9 BB:9 is pretty impressive so far. Their bullpen has been pretty decent too. Fielding-wise, Milwaukee is actually one spot ahead of the Cardinals so far, good for 8th in MLB. Despite this, they are tied with the Pirates so far in the season.
What's left? The NL West... The Giants are in first out there, with a very impressive bullpen and great starters. Their fielding is not going to save them many runs, but with great pitching across the board, do they need it that much? Offensively, they have been the victim of a .280 BABIP, but maybe they are just not very good at hitting. Their .297 team wOBA seems to agree with that sentiment. The 2nd place Rockies have been a little better offensively with a .313 wOBA (.275 BABIP). They are also much better at fielding.... BUT, their pitching is pretty weak thus far. They are rocking a .269 BABIP, but are still only ahead of 7 teams in the majors in pitching.
Back to the Royals... I mentioned them briefly, but you look at their 7.5 team WAR and it is good for 6th in the majors on offense. However, their pitching has been even more impressive, but in a bad way. 2nd worst pitching in the majors by WAR. Their fielding is average, so this team will probably just finish in 3rd place at best I'd guess. The last place team in the AL Central is suprisingly the Twins, the worst hitting team in MLB. They have been pretty unlucky in BABIP though at .264. Here are the most unfortunate teams in MLB offensively.
And the most fortunate pitching staffs. (all stats courtesy of fangraphs.com)