I never really got the whole rivalry between DC and Marvel fans. It's even more meaningless than the whole console war thing.
I like both for different reasons. When it comes to the universe as a whole, I prefer the Marvel 616 to the DCU. Marvel just seems to have a much smoother and equally distributed power curve, which in my opinion makes the big picture more interesting. This is also why I prefer the big Marvel events to the big DC events. Marvel just has a better sense of scale.
However when it comes to individual series, I prefer DC (especially the DC imprints like Vertigo and Wildstorm). Almost all of my favourite American comics are DC: Planetary, Hellblazer, Transmetropolitan, etc.
Also, I'm slightly disappointed that in a poll about American comics, there's no mention of Dark Horse or Image Comics. I mean, come on: Invincible, Hellboy, Usagi Yojimbo? Anyone?