I much prefer DC. Not that I have anything against Marvel per se, and I consider Stan Lee a personal hero, but I have always (and by saying always I'm going back to the 1970s here) preferred how DC's characters were handled, presented, and the storylines were generally more solid. There were always exceptions, but given the choice I always seemed to gravitate towards DC.
When I started buying comics again about 8-9 years ago (I'd stopped except for a few select titles for most of the late 1990s) I was drawn in by the mature storytelling and storylines of the DCs - specifically, I was brought back by the then-current Legion of Superheroes reboot and Identity Crisis, the latter being the closest thing to Watchmen outside of Watchmen that I've seen (and Watchmen itself was a DC release, it's worth noting). I tried getting into Marvel, but it just never caught on with me. There have been a few titles - Black Widow is one and I followed She-Hulk for a while - that caught my attention and I kept reading. But I never had any interest in Captain America or the Avengers or even Spiderman to the same degree as the DC equivalents.
I still buy my stack of comics every Wednesday, and while I never ignore the Marvels, except for stories involving Black Widow and the occasional other character, I can probably count on two hands the number of Marvels I've bought in the last year, as opposed to the dozens of DCs.
One area where Marvel excels is in getting live-action movies done of its characters. DC is frustratingly slow in that area. But at the same time, the DCU movies kick ass.
Looking back, DC also gets bonus points for being the company that put out a Modesty Blaise graphic novel, as well as a sequel to The Prisoner TV series.
Alex