I would go with Yoruichi.
From my point of view she is the sexiest, the smartest female character so far. I really like her powers, her character and also it was funny to see her a bit perverted in SS Arc, when she tried to seduce Ichigo a bit.:))
Her character gives the impression of being developped and thought-through. She has a backstory. She's useful for more than just fighting and comic relief. She's not annoying nor is she cliche.
Yoruichi definitely :)
She's my fav female character and i like that she's very strong
Orihime Inoue. She's just not this nice girl that's being portrayed as of now. Not saying she's mean or anything. But there's more to her character and potential. There's more to her powers as well.
yorouchi,she is strong,cool and smart,and her behavior was awesome