Ruffalo was the best to me of the ones listed. Bill Bixby would be my choice if he was in the poll. Of course that would be unfair because he had much longer to play Banner. Even then he really played a fine Bruce Banner. He was smart, tortured with trying to keep the beast within, and man oh man were his transformations great! Everyone has acted out a Bixby transformation at least once, and if you haven't you have no soul.
Bana played in what's my favorite Hulk movie. I absolutely love Ang's Hulk. It's so deep, and the characters are well done and multifaceted. One of my only problems with the movie is Bana. He plays the repressed part correctly, but he plays it too much. It's like he's whispering the whole movie. His transformations were great though. Next to Bixby I think that his were the best.
Norton was good. He came across very Bixby like, but the problem with the Incredible Hulk movie is that there isn't much to it. There's not much build up, character depth, and the Hulk looks really terrible. He looks like a roided up piece of vomit. But when it comes to the Banner portrayal Norton does well with it. He's a talented actor after all. He's just not as memorable as he could be, but that's no biggie.
Ruffalo was excellent. His Banner was intelligent, but you can tell he was so used to being repressed. He really spoke as if he was a guy that really didn't want to let loose on anything, so he's a bit overly nice like you would expect Banner to be like. One thing I loved about the movie is that they went to great lengths to show Banner's intelligence. The only problem is that the transformations were a bit weak. When Banner transforms into Hulk it's supposed to be this epic event that unleashes a ton of rage. In the Avengers it just sort of happens. He was still cool as hell though.