Rough choice, but i'll go for Karin.
I didn't like how they portrayed Karin, i mean, she has some good skills like chakra sensing at long range, but besides that she's completely useless!!
Not to mention her personality, which is 99.9% based on her crush on Sasuke, i mean, c'mon!! we need more than that, otherwise is like she's just a b!tch who wants Sasuke to have her (in all ways possible)
However, it seems she'll be changing since Sasuke almost killed her, so maybe i'll like her better in the future, i guess i'll have to wait...