Hmm... I don't write characters I don't like so I don't know if I really have the least favourite one as such. What character I like to write depends a lot from my mood. Sometimes I'm all GRR and prefer to write characters who are a little (or a lot) toppy, or even evil, not-human or insane. I really like writing someone whose thought processes are a little hinged.

Of course, other times I'm feeling the opposite of grr and want to write someone a little uncertain but brave. And funny. And weird.

Sigh, this is like the vaguest answer ever. Sorry.