Quote by LiquidMatthew
Mark Hamill. How is he not even a choice in the poll? http://www.youtube.com/watch?v=_gBWpWwIBKw
That's what I was going to say, too. For those not in the know, Hamill (best known as Luke in Star Wars) started voicing The Joker in Batman : The Animated Series a couple decades back and has reprised the role for other animated shows and (I think) videogames since. He does an amazing job in the role.
Of the options given, I actually went with Romero (I'm a fan of the Adam West series) but will also concede that I haven't seen Ledger's performance in Dark Knight yet.