Marvel is going to be more "successful" than DC (if by successful you mean Diamond orders) pretty generally, I think.
1) Marvel HAS to be. They're a publicly traded company, on their own essentially.
2) Marvel has certain franchises (X-Men, Spider-Man) that are always going to be successful, and appeal to a wide range of readers. Also, the more down to Earth nature of Marvel as a milieu probably helps.
All that being said, DC Comics is part of a massive multi-national entertainment conglomerate. What T-W wants out of DC is some profit on the comics side, and the ability to make more cash on licensing DC property.
From a business perspective (as opposed to a msg board fanboy perspective) if DC is managing to bring in some money with individual issues, trades, HCs, and the rest, then it's gravy. How they match up to Marvel, I shouldn't think, is much of a concern to the board members of Time Warner.