Her sad, defeated smile in #4 really gets to me.

I think I like #2 the best. That attitude suits her.

I'd say #3 fits her more now that the latest manga show that she gets nervous or loudly insecure whenever her appearance, intelligence or simply the subject of love is discussed.

Not to small or big so 2.

#2 or 3 seems to be the more canon imagery for most characters. But in this case I think 3 and 4 meshes well personality wise and since I'm a sucker for big boobs... 3.5