I don't know that there are any characters in my fandom that I dislike writing. If there were, I'd probably just avoid writing them. Some of them come more easily to me than others, of course: I used to have trouble with Gippal and Yuna, still sometimes have difficulty with Fran, and in my newer fandoms there are plenty of characters that I just haven't worked with yet.
My favorites, in terms of both enjoying writing them and feeling like it comes easily to do so, are Auron and Paine in FFX/X-2 and Balthier in FFXII.
12. In what story did you feel you did the best job of worldbuilding? Any side-notes on it you'd like to share?
Hands down, AGL. I already talked about this, in my answer to the very first question. The effort I put into building out the world of Spira gave me a framework that I continue to use in my FFX/X-2 stories to this day. Since I've gone back to this world so many times, I'm hard pressed to think of any details that haven't worked their way into one story or another, so instead, I'll open it up for questions, character-backstory meme style, except the character is Spira. Ask me about a place, an institution, a historical fact, whatever, and I'll give you some details about it from this universe.
30 Days of Writing: Complete list of questions
This entry is also posted at http://owlmoose.dreamwidth.org/484084.html. There are currently comments on DW.