I don't know if you guys saw Young Justice, but having Brent Spiner from Star Trek: TNG as the Joker wasn't a good casting choice. I would have gotten Guil Lunde or Paul Sidello from New Cutey Honey instead.
For my money, the worst Joker was Michael Emerson, the little nerd from Person of Interest. He portrayed him as Paul Lynde, making for a gut-wrenching experience.