I think Heath Ledgers version of the Joker was interesting. I didn't really like the other ones.

I would guess that he's actually the "Dark Knight." From the way the movie portrays him, it seems he's a ex-military guy that lost his mind. Technically he does more for the city than Batman by basically pitting criminals against each other and going after corrupt officials. So I did dissect the meanings in that movie, my buddy was really into superhero movies and such but I usually got bored with them; I would say that's the only one I enjoyed.