...to me, has to be Mr. Burns.
I mean, think about it.
Time and again, people talk about their fav's being Hans Moleman, or Lionel Hutz, or Ralph Wiggum...and that's fine and dandy.
But really...without Mr. Burns, there'd be little conflict. His cartoonish super-villainy gives Springfieldians soemthing to hate. His out of touchness gives us something to guffaw over. His frequent turns of heart give us something to smile about.
...plus, he gets all the best lines.
I'd like to see a list of "Burns-isms", myself...