I'll have to say quality too, though I do intend to buy every Mega Man title I can, which may be perceived as quantity. Mega Man's my obsession, so to me it's still about quality.
I've rarely sold a game, and if I did so, I had to really hate the game, or at least lose all interest. Either that or it was a duplicate. I think I've sold back 5-7 games (leaving me with roughly 200+), and they were all more recent titles (DS and Wii titles).