Man, making me choose between ninjas? That's just cruel.
Ryu was probably the freshest in my mind, I must've gone through NG three or four times (including once in his future suit).
I like Ayane too though, more from DOA than NG, as she's got that kind of underdog-in-a-tight-spot thing that appeals to me. Definitely a favourite (and for reasons other than boobies, TYVM).
Sub-Zero's an old favourite tho, since way back. My first (and biggest) taste of the MK franchise before it went to shit (anywhere after MKII), he fills me with nostalgia.
But hey, here's one: Speedy Ser-vi-ce. The Pizza Cats were originally ninja, not samurai...
EDIT: Good question, where the hell IS Dr Mc Ninja on this list?