Top 20 impact prospects for 2013

Here's my third annual ranking of the top prospects based solely on their expected impact in 2013, a list that factors in expected roles and playing time as well as my expectations for their immediate performance.

For all the talk and hand-wringing about teams overvaluing their prospects, the reality shown on MLB depth charts right now is that there are almost no rookies currently locked into major league jobs for 2013 -- seven, by my count, if we're talking about just every-day position players, starting pitchers and closers, including two Marlins who have their jobs only by default.

There are a number of rookies contending for jobs this spring, of course, but most of the impact we see from rookies in the majors in 2013 will come from players who are called up in May or more likely June as teams attempt to manipulate service time while giving at-bats and innings to "proven veterans" who "play the right way."

As in previous years, I have excluded players coming from other major professional leagues in Japan and Korea. They are rookies but are too experienced to consider alongside rookies who have come up through MLB farm systems.

1. Adam Eaton | CF, Arizona Diamondbacks

Eaton has one thing no other top-100 position player prospect has in 2013: a full-time job, most likely playing center field for the Diamondbacks and leading off. While the team loves him because he is scrappy and gritty and plays hard and stuff, he also takes great at-bats, makes hard line-drive contact, and has improved his conditioning and agility to the point that he can handle center field if he improves his reads. A favorable ballpark also will help his candidacy for rookie of the year.

2. Shelby Miller | RHP, St. Louis Cardinals

Chris Carpenter's injury should give Miller a rotation spot, although he'll face competition from Joe Kelly and fellow rookie Trevor Rosenthal. Miller has the best present arsenal of the three and was dominant after some midyear adjustments to his delivery in 2012. He'll miss a lot of bats even if his command is inconsistent, but I do worry about the somewhat flat fastball making him homer-prone.