I don't even see potential. Wang throws just as hard as Beckett, gives up less homeruns, has better control. I don't see Beckett better in any way shape or form.
Mussina > Schilling
Wang
Pettite
Johnson
Igawa/Pavano
The question is not who is number one, etc. The only ones that really matter are 1-4. No one goes with a fifth in the playoffs. However, I will include all 5.
So, the Yankees sport Wang, Mussina, Pettitte, Johnson, and Igawa/Pavano. The Red Sox sport Schilling, Matsuzaka, Beckett, Papelbon, Wakefield.
In the matchups of number one's, Wang tops anything on either side. Let's put him up against Beckett, since that seems to be the consensus in this argument. No contest. Edge: Big-Yankees.
Schilling versus Mussina. Both pitchers are getting up there in years, but Mussina had been more consistent. Edge: Yankees...very slight.
Matsuzaka vs Pettitte. Toughest one to call. Pettitte comes with a track record, Matsuzaka could be boom or bust. Pettitte has the pedigree, Matsuzaka has the hype. No one really knows this one. Edge: pick'em [i know Sox fans will disagree, but this could go anywhere from huge edge yanks to huge edge/no contest sox]. No one really knows.
Papelbon vs Johnson. Johnson was the benificiary of a potent Yankees offense. Papelbon was dominant in the pen, but problems with his shoulder lead to question marks. However, I will take Papelbon's youth and skill. It's not like Randy Johnson is the most durable these days either. Edge: Red Sox.
Wakefield vs the 2 headed monster. Wakefield will put up the same numbers he does every year. The combination of Igawa and Pavano should yield about the same results as Wakefield does alone. Edge: Who cares?
I admit, the Sox rotation has more potential, as they have 3 starters under 30 and are still maturing, against the Yankees one in Wang. However, going into next season, I think there is a slight edge to the Yankees only because of the unknown of Matsuzaka. If he comes as advertised, then the edge is huge to the Red Sox.