The only character That annoyed me from start to finish was Yarne for how whiny and cowardly he was.
I liked Vaike at first, but he needed to grow past his 'Vaikeness' to not be annoying later on. It got old.
I found Sumia harder to keep alive than Donnel for some reason, which made me not use her even on casual mode. Donnel is also a real pain to get to be useful, but I don't have a problem with their characters. I just don't like using them in battle.
For the most part I like the personalities of the characters and find the villains to be inoffensive to pretty good. I find the supports to help a lot in fleshing out the characters when they aren't always in such a serious situation.