I saw everyone of them at KCon this year. (Except Two-Face; can't remember if I saw one or not). And KCon was in Portland for the last three years.
I'm not planning on doing it, but if I were to, it'd be as the Riddler. He's my favorite and, as my girlfriend pointed out to me once, he's the only one who became a villian by choice, because he was bored. Not that I agree with it, but that's kind of cool.