Hinata, hands down. She's cute, has an awesome power, shows a lot of character development (non-innuendo), and dresses more modestly than pretty much any other kunoichi in the series except Tsunade.
Secondary...Gaara. Awesome power, starts off as bloodthirsty psychopath, but as he eventually gets over his major psychological hangups and starts atoning for his past actions, he's really a great guy.
Honorable mention to Shikamaru and Shino, the first for being a lazy genius who grows out of the "lazy" aspect, and the second for being an underused badass with a wonderfully creepy power.