Although I often pick the short girls, in this case, I'm picking Team Fox. I think Beyonce tips the scales on this one.
Specifically, I pick Megan Fox to lose to both Carrie Underwood and Li'l Kim, and I pick Beyonce to beat both Carrie and Li'l Kim. This may sound like a draw, but it's advantage Team Fox because Beyonce can beat the toughest girls on Team Underwood whereas the toughest Team Underwood girls can only beat the weakest Team Fox girl.