I prefer Mark Hamill over all due to his voice in the DCUA and along with Arkham Asylum.
Number 2, would then be of course Heath Ledger on how he really brought the Joker to life in the live action movies.
Then of course you guys probably won't like what I'm about to say but I would prefer any other joker after these two, besides JACK NICHOLSON.
My reason why is because it seemed like just another movie roll of him just asking as of course Jack Nicholson......He didn't bring any feel to the character at all and I found him rather boring. Even though the long hand gun he pulls out of his pants was entertaining. I just can see any of the other Jokers pulling that off even better.
__________________ When Gotham is in ashes, you'll have my permission to die - Bane
If Mark Hamil's were live action, he'd get my vote, but I'm going with Heath Ledger on this one. His interpretation of the character just has every single characteristic I've wanted the Joker to have on the big screen.