Prior, not good enough to be an ace? He was the best pitcher in the history of college baseball. He's been outstanding in his first pro season. He pitched a complete game last time out that would have been a shutout had Mark Bellhorn not made a bad decision, K'ing 13. He's just awesome, and will be as good as Roger, Schilling, etc., are now, in the future.
Right now, I think Randy Johnson is the best pitcher in baseball. No doubt he's the most intimidating. When he's on, it's just sick. And when he's off, he proves that he's a vet that knows what he's doing and can go with what he's got for a day and STILL shut another team out. In the future, I think Mark Prior, Josh Beckett, Ben Sheets, Roy Oswalt, Freddy Garcia, Barry Zito, Mark Mulder, Joel Pineiro, Kerry Wood, Carlos E. Hernandez, and Jason Marquis will be the elite pitchers, and I'm sure I forgot a couple. IMO Freddy Garcia could become the best pitcher in baseball at any time now, but in the long run, Prior will be the best of the above.