I wish I could explain why I like DC over Marvel. I started out with DC, reading Batman and Superman comics as a kid. Maybe it's their iconic status that keeps me loyal to them. Spider-Man and the X-Men don't have that. I watched their cartoons as a kid, as I did with Batman and Superman, but they weren't on the same level.
It's not to say I won't enjoy a Marvel comic, as I have a number of them since I started collecting them 8 years ago (when I began undergrad and had unlimited access to 2 comic shops across the street from campus). Recent drastic and unnecessary (IMO) changes to the characters (organic web-shooters was a cool idea, though, while the whole Gwen Stacy/Norman Osborn thing wasn't...and the beginning of JMS' run on Amazing Spider-Man was good) and incredible delays on titles with no accountability sapped my interest in Marvel. Quesada seems more interested in sales than quality and is going to the summer blockbuster route with stories - produce something with a lot of bang and flash to keep readers buying more and more.
Something DC and Marvel are doing that really loses my interest is the universe-wide crossovers. I've no confidence that I could pick up a DC comic and know what is going on, save for Batman (though this RIP stuff doesn't seem to be something I want to read, as it may change the foundations of Batman, which I have no interest in reading) and All Star Superman (being outside the DCU).
If I had much discretionary income to work with, cool. But I'm not going to drop $2.99/$3.99 on a book anymore for 22 pages. The prices of Marvel TPBs suck, too, and I've never bought one for that reason.