I'm glad this thread was resurrected, it's a great matchup! Really difficult to decide a winner between the two when you think of it because, like I said, it's a great matchup.
I'm pretty sure that between these two a fight would get pretty damn catty, especially if it involves throwing around the words "Who's the better girl on the track" and such. Knowing that, I think it would get really vicious really quick with both quickly throwing out all stops. When Allison is in control, I'd like to think that she would go after Michelle's boobs because she sure likes to flaunt them in pictures. Michelle however would work Allison's nice abs down and eventually break them just because I think Michelle would have more overall stamina.
In the end, I vote for a very battered and tired Michelle sitting on Allison's face, smothering her into unconsciousness as she does that adorable little hip shake dance and smiles as best she can.