The short answer to this question, in my opinion, is Heath Ledger. However, I say so based on the fact that Ledger’s performance amplifies the elements of the Joker’s established character that I find appealing and downplays the elements I don’t. In short, he’s closer to the Joker I took from the comic books but I can totally understand why he might not be like the Joker other’s imagine.
One of the most notable things about Heath Ledger’s portrayal of the Joker in Christopher Nolan’s The Dark Knight, is that the character is presented as being mentally ill. He is plainly a damaged person but also one of deep psychological and philosophical understanding; justifying his attempts at driving the citizens of Gotham mad via a carefully constructed concept of true chaos theory that just somehow doesn’t cover-up the reality of him just wanting to prove that others would break the same way he did if they experienced trauma similar to his. Ledger’s Joker is also far darker than any that have been seen before; vicious and cruel he delights in the intimidation, anguish and pain of others. In short, Ledger’s Joker is a Joker for the real world, dark, gritty, violent, terrifying and unpredictable.
Jack Nicholson’s portrayal of the Joker in Tim Burton’s Batman The Movie however, was much more gentle. Nicholson’s Joker was visually lifted strait from the pages of DC’s comic books, possessing a simultaneously intimidating yet fascinating impossibly wide grin (rather than Ledger’s Chelsea-smile). Likewise, Nicholson’s joker had a back-story more in keeping with the comic books (or rather the events portrayed in Alan Moore’s The Killing Joke) while the Joker seen in The Dark Knight has no back-story beyond his own schizophrenic (or perhaps just plain erroneous) recounting of how he came to be so disfigured. But again, that factor is one that I appreciated in The Dark Knight, I liked that element of unknowable uncertainty about the man’s character. He’s not sane, he’s not logical in the same way that your average person is and even if you were given his whole background, you’d never truly understand him, and even if you did this would only serve to rob him of his mystery.
There’s also the matter of acting style. I am a great fan of Jack Nicholson but his range of acting seems to only incorporate playing Jack Nicholson in whatever situation his character happens to find himself. Ledger’s performance on the other hand was wildly different from those of his previous roles and his Joker was truly unique. He seemed to leave his ego, celebrity and personality at the door and let the character he was playing take the centre stage.
Of course, Batman The Movie and The Dark Knight are two completely different films and Jack Nicholson’s Joker would have been just as laughable in Nolan’s work as Ledger’s would have been in Burton’s (and I don’t mean the good kind of laughable). Nicholson’s Joker was fun, imitable and charming. Ledger’s was terrifying, dangerous and perhaps worst of all believable.
In today’s world of atrocity and inhumanity Nicholson’s Joker would pose no more a threat than the average criminal whereas Ledger’s was intelligent and cunning enough to scare even the hardiest of citizens.
In conclusion, I stick by my original opinion of Heath Ledger providing a better portrayal as the Joker. Not only that but a great portrayal in general. If he isn’t at least posthumously nominated for a Best Actor Academy Award, there’s just no justice in this crazy world.