Kasumi vs Ayane vs Momiji?? Kasumi doesn't have a chance of winning lmao. Kasumi's been running and fighting for a long time now while in that time Ayane's been training, killing fiends, and fighting. The only real advantage Kasumi has is in the fight is probably evasiveness. Ayane would have the biggest advantage in speed, Momiji would probably have the most brute strength since she was trained bye Jesusbusa himself. I'd say Momiji would emerge victorious in this fight orz..
Eh? You are aware that being a runaway ninja involves fighting for your life every day right? training & fighting fiends as opposed to sleeping with one eye open. Not to say fiends in the NG/DOA universe are everywhere, I highly doubt Kasumi would be lucky enough to never come across any during her time running away from highly skilled ninja ( I'm gonna be a total nerd and state they're on the equivalent of Anbu from Naruto. Which is basically the best of the best. Trained to kill. )
The only thing that would possibly get Kasumi killed is her hesitance to actually kill. Other than that, she's got all of them beaten easily. She was leader of the mugen tenshin clan for a short period =\ so she was literally the leader of a ninja clan.... c'mon... lol =\
Not to mention the history of DOA proves that Kasumi is stronger than Ayane -_- Ayane wanted her dead in DOA2 and Kasumi still won. And Kasumi didn't have the intent to kill. Which is the point I was making, she wins even without wanting to. If she was forced to, I'm pretty sure she'd be a force to be reckoned with.
~ and also Momiji, like I said we don't know enough about her to place her. But from what we've seen and heard, no. She'd be the worst of the 3... at the moment.