Reading most of these replies you can smell a mile off either these are old readers (with old ideas) or not reading both (or either for that matter) publishers.
Personally I started with Marvel (and reading comics in general) about a year or two ago. Recently in the past few months I've moved more towards DC.
I'm a fan of Deadpool, was reading Thunderbolts; X-Force & Cable; Thanos old and new; moved to Superior Spiderman around issue 19; as well as a couple of random things here and there.
DC, I started reading Batman and Swamp Thing, to be honest it's Scott Snyder in general, I mean, I never saw myself being a fan of Batman, I still have issues with the character but I can't get enough of Snyder's characterisation. I also read just about anything Vertigo; followed some Forever Evil; Batwoman; Animal Man; Sandman Overture etc.
Okay, with that out of the way... The biggest difference I found and the reason I moved to DC was because, well, like most comic book fans - I'm a 20-something male. DC and particularly Vertigo, deal more in adult themes and build greater mythology. Marvel is too narrow, aimed at children and just doesn't connect with me as an adult reader.
For instance, Spiderman is a series I never saw myself reading (it's themes are below me and too aimed at children/teenagers), but Superior was genuinely different and I won't be reading the upcoming Amazing series. Superior for me though reinvented the character, bringing him into a more adult framework - his new love interest is not the typical "hot girl-next-door", she's intelligent, a midget, but 'Peter' is with her not for her physicality but intelligence and creating a more meaningful relationship. He's moving forwards in life, working towards a PhD.
It also explored the ramifications of killing foes, something I think makes sense - why would you let a wild dog run free time and time again, completely aware that saving one "lost" life (the perpetrator) you risk a hundred innocent lives being lost? Even if you disagree, at least it opened a discussion up, potentially aspiring us to redefine modern morals within comics.
Thunderbolts, welllll, look, it was a bad book, purely poor writing and extremely bad art. Whoever said the editors at Marvel are decent you need to read this series, then reevaluate that statement. It was terrible, Soule is a very capable writer and seems to be doing a pretty good job of turning the series around.
The number of X and Avenger titles is just simply overwhelming, as a fan of neither even trying to keep up with any of those series would just cause unnecessary headaches, a major hit to my wallet and no real worthwhile story telling.
Okay, so I've been pretty harsh with Marvel so far but *personally* DC is my new camp (if I'm to choose).
That doesn't mean everything they produce is top notch, though everything I've explored so far I've been happy with. That's not me being selective, egotistical, etc. Everything I've read has been enjoyable, nothing has felt like a struggle or worthless.
I argue you to pick up Batman and Superior Spiderman (the two biggest selling titles from both publishers over the past year), as an adult reader to not find the writing and artwork from Batman head and shoulders above Spidey.
Finally, don't be convinced by the "X publisher deals more in reality and Y is fantasy". Look, you're reading comics to escape reality, to explore ideas other mediums aren't capable of, whether you're a child or an adult. All good stories will contain some level of meta-narrative (teenage issues; adult themes; religion; philosophy; etc.), if you can't find it and want it the story isn't for you. If you don't want it, then find what you think is cool.
The biggest distinction between Marvel and DC right now is that the former is catering to a market < 16, the latter is geared to those > 16. DC is building more intelligent worlds, characters and wanting to shake-up and rebuild everything. Marvel is very focused on keeping the status quo.
DC is focusing on villains, darker elements of story-telling and utilising them as a means to introduce and redefine characters. Marvel is building more towards the casual market, pushing everything more into a film tie-in basis, with increased numbers of superfluous X and Avenger titles, as well as finding ways to build more Thanos stories and expanding their cosmic-verse.