So I'll be the first to say it, Raging Bull is better. Rocky is great, but as a piece of film making I don't see why you couldn't say the former was better. Stylistically and thematically it's far more impressive and interesting, it has a better leading performance, it's Scorsese at the top end of his game. Such a brilliant character study. This isn't a knock on Rocky, it's just that I feel Bull has far more to offer as a film. I don't think just because two films are different they can't be compared in quality especially in a case like this where to me one has a clear edge for me personally. Sometimes that can be the case but for me this isn't one of them.
You're so going out on a limb by saying Raging Bull is better. Good job taking a stand.
What more specifically does Raging Bull have to offer? Any theme you bring up will probably be in stark contrast to themes in Rocky.
Is self destruction really that much more interesting than the underdog defying the odds? Is Jake being a total fucking dick to everyone is his life really that much more interesting than Rocky being a stand up guy? Are the two characters polar opposites? When are your left hand?
Technically, yeah Raging Bull is better. I'm sure its budget was higher as well. Yeah Scorsese is a master filmmaker. He's awesome etc.
If you're going to compare the two, then compare them on how well each does what they're trying to do. Rocky hits a grand slam. Raging Bull is kinda boring, impressive looking, but ultimately pretty damn dull. It's still effective, but the elation that Rocky brings is greater than the morose melancholy of Raging Bull. This isn't to say depressing movies can't be amazing and immensely entertaining. They can be, but Raging Bull isn't actually one of these.
Really though, I still say comparing these two movies to find which is "better" is like comparing It Happened One Night and 2001: A Space Odyssey.