I honestly think the only character I dislike (from having read a large portion of translated supports, watching gameplay footage, etc..) is Aqua.
I mean, Camilla isn't 'that' bad, she's just a little deranged. She even redeems her slightly bad qualities in some supports. But Aqua really just annoys me. Plus the fact that she's completely idiotic throughout the whole plot doesn't help her case at all. Then there's the fact that she's only really good for dancing, and I would rather bring a unit who can kill stuff than bring a unit who can only dance. Dancing and being able to fight are fine, but it looks like Aqua's not got any real combat potential.