Between the two, Batman. Iron Man was great fun, but it didn't have anything like the kind of depth Batman had. I mean . . . seriously, the villains in Iron Man were ---smurfing--- laughably ridiculous. It's a comic book movie, I know. I know. And I loved it. But seriously . . . ---smurfing--- retarded.
However, neither of them would get my pick for best picture. Off the top of my head movies I saw that were better than those include Burn After Reading, Let the Right One In, Slumdog Millionaire. Milk and The Wrestler also look very good. And that Button movie with Brad Pitt looks like it might be really good.