Re: Why Mark Ruffalo?
I like both Norton and Ruffalo.
As a poster mentioned earlier, Norton portrayed the Bruce that was tormented by what was living inside of him, and Ruffalo portrayed the in-control Bruce.
As for the Hulks, Norton's was my favorite. In terms of design at least. That particular Hulk seemed weak, or maybe too grounded, I dunno. Ruffalo's Hulk design was my least favorite, but he seemed much more powerful.
Of course both Hulk's powers pale in comparison to the 2003's Hulk's.