We're very much still at the stage where things are in flux with college and high school prospects. There will of course be ahandful of guys who were considered Top 10 Prospects who will fall and just as many who will 'come out of nowhere' to take their place.
In this post Callis mentions a conversation with a scout who identified Byron Buxton as the #1 talent in the draft and Kyle Zimmer as the top pitching prospect.
He also notes his Top Power/Speed/Hitting Prospects in the minors. Josh Bell gets an Honorable Mention for Power (he's one of his 'Youngsters To Watch')
Finally he offers his list of 11 pitchers who could be #1 starters. The Pirates, along with the Dbacks and Mariners are the only team with two.