***WARNING: BATMAN:TDK SPOILERS AHEAD, FOR THE THREE OF YOU WHO HAVEN'T SEEN IT.***
I disagree with your first point. I believe it's possible to be objective in terms of judging actors' performances, especially in this case. Ledger played the masochist/anarchist to a 'T.' He made you believe, especially in the face of all the doubts about him being a good Joker. For me, the scene in the interrogation room between him and Batman pushed it over the top. Batman pummels him over and over and, the harder he gets hit, the more Joker laughs. Makes Rorschach's death scene look amateurish by comparison.
His discussion with the badly-burned Harvey where he explains his motivation was pitch-perfect, too. He deserved the Oscar, death or not; clearly it was the best performance of the year, by any actor in a movie role, including all of the Best Actor nominees.
No matter how much or how little material an actor has available, he has to bring the character to life. Heath Ledger was the Joker.
I think a lot of people do have a big problem discussing this objectively, on a Watchmen fanboy board, mere weeks after that film's release. These kind of arguments/discussions are really only worth anything when both films have had some time to breathe and soak in.
I agree, Heath certainly wasn't great solely because of the material. He took it and made it his own.
What I meant was, Haley just doesn't have as much to work with and doesn't have nearly as much screen time or moments to shine.
As good as Haley was, his performance is more about a few moments of shining really bright (i.e. the shrink sessions, the ending) mixed with some average moments covered in a mask that doesn't really allow him to emote fully. Yes, he does a good job with the body language, and many scenes with the mask he does amazing things with some rather ho-hum lines. His delivery of "when we were partners" as he's leaving down Dan's tunnel was particularly awe-inspiring.
But for my money, he just doesn't "light up" the screen like Ledger did, even in his absolute best moments. And then there's moments where I felt he was just underwhelming (i.e. the Rockefeller Base scene with Manhattan and Laurie).
There wasn't one single moment of Ledger's performance that was anything other than inspired perfection. That's why he took home an Oscar for playing The Joker of all characters. And while there's no way to prove it, he certainly would've taken that trophy home and received all the same adulation and praise if he was still here today.
I think you'd be very hard pressed to find a working actor (i.e. someone who really knows the craft and what it takes) who feels like Haley gave a better performance than Ledger.