For Gale, I say Slytherin. He's clearly shows he has leadership skills and has that "it's all about what I want" attitude throughout the books. In MJ, we even get to see how cunning Gale is (not going to say anything due to spoilers) and even cruel he can be to people just to get what he wants. Some might argue that it's because he's brave, but I think underneath it all he's not doing the things he does for other people, but for himself out of anger. He is a slytherin to me.