But DC's villains are much more prominent, well-known/loved, than Marvel's. How can Marvel villains ever rival the popularity of Joker, Penguin, Catwoman, Bizarro Superman, Poison Ivy, and Lex Luthor?
I would also have to agree with the comments about the Martian Manhumter having often played prominent roles.
Really, DC's Big Three has become DC's Big Four, with the push for Green Lantern in the last decade or two. And in reality, of those four, Wonder Woman is the one who cannot seem to make it in her own title very well - she needs the other three much more than they need her.