I don't think Batman would make "true" friends with anyone in the Marvel U, and he'd certainly consider some of them dangerous criminals themselves. He might utilize certain characters, like Cap, Iron Man, Spidey and probably even The Hulk, but I can't see him being too chummy with most of 'em. And you can be damned sure he'd have thick-as-phonebook files on ALL of 'em.
Except maybe T'challa. Bats & Black Panther might get along.