I think Heath Ledger's Joker is by far the best. No question. Hands down. You lose Jack Nicholson.
If you haven't seen it yet there might be spoilers ahead...but not enough to really ruin the movie... but you've been warned!
There are too many favorite scenes and awesome one liners to mention. But there is one thing I want to point out and urge you to pay more attention to if/when you see it for the second time. The music/score to this movie is amazing! James Newton Howard and Hans Zimmer (two composers I just learned. Thanks Google) are geniuses! The part that I wish I could record and replay over and over again is the background music to the scene where Harvey Two-Face has Jim Gordon's son by the neck with a gun pointed to his head, and then he flips a coin and points it to his own head... I can't explain it. Obviously you have to hear listen to it. The music really made that scene. If I could listen to something for the rest of my life, it would be that part of the soundtrack. Gahh. Everything about this movie was soo good!
I feel really silly doing this whole blog thing.