Evangeline would have been incredibly comfortable in Ravenclaw, but she's far more of a natural leader. She belongs in Slytherin. If you want to get down to universe comparisons, Evangeline is likely to be the pureblood traditionalist who has uncomfortable feelings about Muggle-borns being allowed at Hogwarts, but wouldn't go to war over blood purity because she's too practical to think that that's useful or smart.
She's a pragmatist, and she's the sort of person who will save herself above others because she does feel like she's an exception to a rule, because she's in a certain position where it's more important that she stay alive -- that is, if she had to choose between a bus of random schoolchildren or herself, she'd save herself, because those random schoolchildren can't make important decisions for the school or the X-Men in a time of crisis. (I'd also argue that this sort of logic is also characteristic of a Ravenclaw, I'm not shitting on Slytherins for being the kinds of people who'd kill busloads of schoolchildren.) That's not to say she wouldn't have anguish over it, but Evangeline is the person who makes the hard decisions, and knows that she sometimes has to be the person that people hate in order to get the job done.
The Scarf of Sexual Preference says: Seeking Personal Servant.