I have a lot of games on Direct2Drive, but the truth is given a choice between it or Steam, all things being equal I always opt for the Steam version of a game (Not to mention that in more than one instance recently, the Direct2Drive version I bought WAS the Steam version due to Steamworks). What's really funny is that I have, on more than one occasion, bought a game I had already previously purchased via D2D again via Steam on a Steam sale (I am a massive Steam sale whore...). Crazy, huh?
That seems kind of backwards, as you clearly get less "ownership" of a game with Steam than you do with D2D, but I guess that Steam has sold me on all of its combined features that I find the overall package the preferable choice between the two regardless.
“The greatness of a nation and its moral progress can be judged by the way its animals are treated.”
- Mahatma Gandhi