Suki

I don't really like Katara but she is very well written to the point where I don't really think I can even out-right hate her anymore.

I have a mild dislike for Suki and a little stronger one for Mei, but I still admire them as overall characters because they're written quite well.

^ That's pretty much how I feel about Suki as well.

Ty Lee, Suki and Mai.

Suki is maybe the only exception, but even to some degree, I think she's written good.

IMO, Mai is the only character whom I genuinely criticize because of the poor writing. In the series, she was okay. Impossible to really like, but that might mostly be because of her constantly expressing her boredom (which in return makes me bored of her). In the comics, the writers seem like they're trying to make her more of a complex and *gag* heroic character, but this just makes her seem more of two-faced hypocrite link
This article talks a lot of why I dislike the writing of Mai.

I used to like Mai but she's kind of fading into the dislike territory. I just really hate how she only references to Azula as 'the nutcase' or 'that lunatic'. It just rubs me the wrong way.