Superman's level adjustment is literally incalculable; it keeps changing. I even read one comic (the one right before Superman lets Lois know his secret, or so it looked like) that in the last week, Superman learned more than five new superpowers. Sheesh!
Batman would be extremely high level. Not only is he an amazingly fast-witted athlete (it doesn't matter how athletic you are if you can't calculate your approximate path very quickly while swinging on a batline) but he's also a skilled martial artist, so swift even Red Hood commented on it, is able to fight after having his ribs broken, one of the world's top geniuses (when fighting the Riddler, they trade riddles for fun, and they're not easy riddles either), one of the world's best detectives, an amazing liar, has the ability to charm random NPC women almost as well as James Bond ... sheesh! You could stat him up with DnD or d20 Modern, but he'd be epic level.
Making matters worse, they've both been superheroes a long time (real world time), meaning you would need to crawl through thousands of back issues in order to find out that, yes, Batman does speak Ancient Algonquian fluently (or some other obscure fact).
PS I don't know if Batman can speak Algonquian. It's just an example.
