I don't think there's much of a difference now. Back in the day I thought Marvel had the better written characters, the cooler characters, while DC's characters had the name recognition.
But I think DC did a lot of improving since I was a kid and they are pretty much on an equal footing in terms of coolness factor for me. Granted, Marvel still has the edge, but lately they've just been overdoing their big crossovers and becoming more gimmicky and DC hasn't been as bad about that.
Admittedly my preference for DC has grown over the last several years and I've moved away from Marvel. I've been steadily losing interest since the Heroic Age started.