At the start of every season, there is a constant debate going on amongst fantasy experts regarding where to rank rookie hitters and pitchers. Here is the policy I use, rarely if ever do I draft a rookie hitter. However, if a player starts in minors and spends a month or so there and gets called up around May/June, then I more seriously assess whether he is worth adding. I got this reasoning when watching "Baseball Tonight" a few years ago and I heard Peter Gammons explain why young players traditionally perform differently than others.
Rookies who start the season in the majors are often overwhelmed a majority of the time out of the gate. Their biggest issues revolve around adjusting to major league pitching and thus have problems with their swing and ultimately confidence. On the other hand, rookies who start the season in the minors generally find themselves a good groove once they are called up. They often display good confident swings and better plate discipline simply because they have been locked in down on the faem and are in a decent place mentally when they are brought up to the majors.
A good example of this was seen among last season's hyped rookie third basemen. Alex Gordon, the most hyped rookie third baseman, started the season in the majors while Ryan Braun (second to Gordon in 3B hype) started the season in the minors. The third impact rookie at third base was Josh Fields an afterthought stuck behind Joe Crede in Chicago early on, spent some time in the minors before being eased into the starting 3B when Crede went down with a back injury.
Rick Ankiel is another example of a player who was called up last year and performed better than many predicted. Many said that Ankiel would struggle as a hitter in the majors, especially with strikeouts, and would not be much of a factor. Ankiel had hit 31 home runs with a .271 batting average in AAA, and upon his arrival to the majors he hit 11 home runs with a .284 batting average in only 172 at bats. This is almost exactly what he had been doing in his time in the minor leagues, and shows how a player can come to the majors confident, with added seasoning and be successful.
Thus, when it comes to drafting rookies, be weary. I would rather pick up a free agent rookie hitter who has had some minor league at bats, rather than draft a guy who will be thrown to the wolves in his first year in the bigs. On draft day, you are more often than naught better off going with the veteran bat as they are more of a proven commodity.