play as Ayane, she wins. The accepted story is that Ayane lost. In DOA2 Kasumi fights Ryu and wins if you play as her, but if you fight as Ryu, Kasumi loses.
Well, Canon-wise, Kasumi kills Raidou, so we can assume she never lost any of the fights before that. That, and if Kasumi lost to Ayane, she'd be dead. For the others, it's not as clear.
@PSM_Akali but you should know that kasumi only killed raidou with ryus help. Kasumi is nothing without ryu and I am wondering if she has noticed that <.<.
If Ryu's in a fight, he wins it. If Ryu's not in a fight, he still wins it (such as in the case of Raidou and Omega, as seen in Dimensions).
So yeah. Basically Hayabusa wins everything.