I'm not going to mince words. WoWInterface is the only respectable site out there. WoWAce and Curse gaming have absolutely no respect for author rights. WoWAce has shamefully and actively
enabled code plagiarizers on more than one occasion. As is obvious from the Times Square like ambiance of their site, Curse gaming cares nothing except about maximizing revenue. They will take every bit of author rights they can get away with without generating too much negative PR. You should have seen their original author release form that they came up with when they redesigned their site. It was absurd. And of course, they do not enforce copyright on the sites they own, even if they agree that violations are occurring.
If you like the add-ons you use, support a site that fully supports the authors that make them. And right now, that is only WoWInterface.