Rookies starting pitchers who slotted to be a No. 1 or No. 2 guy always have more potential - as opposed to pitchers who fill out the back end of the rotation.
Will Daniel Schlereth fall into relative obscurity if he doesn't become a closer?
Relief pitchers are not collectible unless at the very least, they have potential to close - if a minor league pitcher doesn't have any starts or saves to his name, then he isn't likely going to be a star [regardless of a player's real-life potential to be useful if he reaches the Major Leagues].
After being a shortstop in college and a third baseman in his rookie season in 2009, Chicago White Sox rookie Gordon Beckham probably has the potential to be a similar player to Dustin Pedroia at second base.
For position players, consider how a team sees a rookie - was an up-and-coming player a highly touted prospect who was a first-round pick or merely a minor leaguer having a good season in the minor leagues getting a courtesy Major League promotion as a reward.
A rookie who will probably have long-term success is probably a player who can plugged into playing one position for the next five to 10 years - rather than a rookie who is already seen as a utility player or a guy who may not be able find an ideal spot on the field to play and if playing in the American League, maybe slotted to be a full-time designated hitter.
For position players, rookies who can play up the middle may have the most potential - maybe a shortstop, since the position is probably the most athletic on the field.