Pettitte the ace?

After seeing Pettitte have a great game against the Mets, and have much success in the past few weeks, many are saying that Pettitte is the ace of the staff. I for one think that Pettitte is not the ace of the Staff. The staff is a fairly good squad, with potential to be great, with Wang. But if Ponson plays well like he did in the Mets game on Friday, he can fill in the whole that Wang, the real ace of the staff left when he got hurt.
So who is the ace of the staff if it is not Pettitte? It is not Mussina either, or Chamberlain yet. It is not Rasner either, or Ponson. Then who is it? The answer is it could be anyone. One any particular night the pitcher could look like the ace.
We have seen Pettitte do what he did yesterday but he also got lit up for 10 runs in Kansas City.
We have seen Rasner pitch some fantastic games, and then he messes up and lets up six or seven runs, in less than five innings.
We have seen Mussina go eight innings of one or 2 run baseball, but we all know what happened last year, when he was not even in the rotation.
We have seen Ponson do what he did on friday, but we also saw what happened in 3 years ago.
And Joba just doesn't have the experience to be called the ace yet.
Everyone can step up and pitch a great game, but it is the constistency that makes players great, if a pitcher throws great great games consistently then he will be considrered the ace.