SLYTHERIN. I'm 100% sure
I've always loved stylish characters and I think people from Slytherin got this. Besides, I don't think they're all bad people, not all of them hate people who aren't pure blood; it's common sense. And just because you don't want to throw yourself in front of a bus doesn't mean you're coward. Usually, what people (from Gryffindor, sorry, guys) call "coward" actually means "smart".
The fact that Tom Riddle was also in this house helps a lot. Go, Voldie!