Add me to the Hamil bandwagon, followed by Nicholson. I feel Ledger is overrated, I liked Ceasar Romero better even with the 'stache
Hamil by far, but that's not quite the same as comparing a live action performance. The animator's deserve a lot (if not most) of the credit for bringing that iteration of the character to life.
Ledger was the best performance, but his Joker was a little too different than what I typically like. So I guess I'll go with Jack for the live action guys. Still need to see way more of Leto to get a proper opinion.