We're a ways away from really discussing who the Rookie of the Year is going to be for either league, but this is always an interesting topic of discussion given that a lot of these guys should end up having pretty bright futures. You'll always get a clunker like Bobby Crosby or Angel Berroa once in a while, but often initial success can be an indicator of a nice career.
Here are how my top-5 ballots would stack up for both leagues if voting occurred today, and people cared about who I voted for.
AMERICAN LEAGUE
(Author's Note: While writing this piece, I used FanGraphs rookie leaderboards in order to compare different players, and they mistakenly included Alexi Ogando as a rookie on these lists. As Adam Morris noted in the comments below, Ogando isn't in fact a rookie, so I've removed him from the list and adjusted things accordingly. Thanks to Adam for noting the mistake.)
5) Jeremy Hellickson, Tampa Bay
After removing Ogando from the list due to the issues explained above, Hellickson snags the No. 5 spot on this list now. It hasn't been a great year for the Rays right-hander as he's adjusted to life in the big leagues, but he's still pitched good enough in nine starts to post a 3.14 ERA with a near-4 FIP. You'd like to see him get more grounders at the MLB level, as his GB rate of roughly 36% is pretty low, and is trademark plus command has left him this year. He should be able to push down his walk total, though, and emerge as a very solid rotation mate to the likes of David Price and James Shields.
4) Jordan Walden, Los Angeles
His command is still shaky, but he's armed with fastball that touches triple digits and a legit out-pitch in his slider, so things are still going well so far for the big reliever. He's 10-for-13 on save opportunities for the season since taking the closer's job from Fernando Rodney and doesn't appear likely to vacate the role any time soon. Among AL relievers with 20+ innings pitched, only Mariano Rivera, Jonathan Papelbon and Glen Perkins have posted better FIP figures than the 23-year-old Walden.
3) J.P. Arencibia, Toronto
So far, Arencibia has been pretty much exactly what people expected: a catcher that can provide some serious thump to a lineup, but without much of an on-base percentage. The 25-year-old has immediately become one of the better offensive catchers in the league and ZiPS projects him to finish the season with 28 doubles and 25 homers, but he's still striking out 26% of the time with an OBP that's hovering near .300. Even with the poor on-base skills he's still an above-average all-around catcher, though.
2) Zach Britton, Baltimore
Britton gets the slight nod over Ogando for the No. 2 spot, but realistically the two pitchers are going toe-for-toe. As expected, the power lefty has proven to be elite at inducing grounders even at the game's highest level, but it remains to be seen whether his low strikeout rate is the sign of a young pitcher that needs to make adjustments or an indication of raw stuff that won't quite miss enough bats to push Britton to an elite level. There's Brandon Webb-type upside here, but at the very least Baltimore has an exceptional mid-rotation innings-eater.
1) Michael Pineda, Seattle
Before the season, some people weren't sure if Pineda had the secondary pitches to be a starter at the major league level yet, but so far the 22-year-old has shown that he's just fine. He's absolutely lighting up radar guns as the hardest-throwing starter in the majors this season, and his 2.26 FIP is tops among all American League starters. His ERA is bound to go up some, but not that much. It really looks like the Mariners may have another ace on their hands.
NATIONAL LEAGUE
5) Wilson Ramos, Washington
Trading reliever Matt Capps to the Twins in exchange for Ramos looked smart when the catcher wasn't taking pitches, but now that he's flashing an 11% walk rate the deal could end up looking pure genius. Scouts have long praised the 23-year-old's work behind the plate and his ability to make contact, but questions about his power and plate discipline were always knocks on his record. This season he's putting a lot of those questions to rest, though, with 14 walks and 11 extra-base hits in his first 34 games. If he can continue to hit anything like this, the Nationals are going to have one of the better catchers in the game for the next few years.
4) Brandon Beachy, Atlanta
His candidacy hasn't been helped by his recent DL stint, which he's still weeks away from returning from, but Beachy's numbers still impress at this point in the season. The undrafted free agent posted a 3.45 ERA in 8 starts with even superior FIP and xFIP figures, and he's showing talent evaluators that his upside may be higher than that of a good back-of-the-rotation starter. Beachy has yet to struggle in his pro career, so it's hard to doubt him at this point, right?
3) Danny Espinosa, Washington
The guy that's one spot higher than Espinosa on this list is getting far more attention thanks to the handy dandy batting average, but a deeper look indicates that the Nationals second baseman's numbers may hold up better long-term. Espinosa's .200 batting average certainly is brutal, but with a solid 9% walk rate and 6 home runs on the season, Espinosa is doing a very solid job of coming through in the other facets of offensive production. His .221 BABIP is bound to go up soon, and when it does his overall line should look a lot better. People may have trouble voting for someone whose batting average sits in the .230-.240 range, but if he's a plus defensive second baseman with 20 homers and 20 steals, that helps right?
2) Darwin Barney, Chicago
Now, Barney's been nothing short of awesome for the Cubs so far, but realistically the second baseman is probably playing over his head a little at this point. He's a good defender at second base and a fantastic contact hitter that rarely swings and misses, but he's a guy that rarely walks and he doesn't produce much power. Unless he can begin to show pitchers that he can punish them for mistakes, he's going to get less to hit as pitchers challenge him to show more patience. Barney should be able to make some adjustments and stick around as a very solid second-division starter, but don't expect him to match Starlin Castro as another rising star on the other side of the keystone.
1) Craig Kimbrel, Atlanta
I know, I know, it's hard for me to get excited about handing the Rookie of the Year award to a relief pitcher, too. But in a year where nobody has really stood yet, Atlanta's closer has truly been one of the game's best at his position. Kimbrel may still get a little wild from time to time and he can improve upon his 14-for-18 mark on save chances, but he's been the best reliever in baseball so far this season according to FIP and xFIP. With a ridiculously good fastball-slider combo, Kimbrel misses loads of bats and rarely offers hitters pitches that can easily be squared up. His career pro numbers are simply insane: in 196 combined innings between the majors and minors, Kimbrel has struck out 318 batters (14.6 K/9) and allowed only 5 home runs (0.22 HR/9).