Marvel is bad**s, but I have to say, I love the characters in DC aswell.
Marvel has the Avengers, SHIELD, bad**s supervillains, epic movies and great games. DC has the Justice League, Teen Titans (apparently I never knew that), awesome supervillains such as Joker and Quinn, and also has great movies and games.
From what I compared with, DC has the better side, but in my Can't Choose defense, only the Batman movies had me interested in DC. Marvel had me in on all the Avengers movies besides Thor, which I didn't like as much.
Games-wise, I can't pick a best because I've only played the first Marvel Ultimate Alliance and Mortal Kombat vs DC.
Overall, I can't take one over the other. I'll probably read the DC comics before the Marvel ones, if I ever do, but that's because I like the characters in DC a little better.