For sheer power in the characters, DC would win hands down. In the marvel universe Kryptonite doesn't exist, so even if Marvel took every other DC character down, Superman could wipe the floor with the rest of them. And before you even say it with the mind controller powers people in Marvel. DC has a built in guard against it with Plastic Man. He has no centralized mind and is not affected by mind control or anything like that. so Xavier and all those guys are screwed.
But in the sense of comics and content, Marvel wins I'd say. DC has been known to have real thought provoking issues, but Marvel has those all over the place and great storylines.
[/nerdular nerdance]