I go back and forth on Derek. Like, there's a part of me that wants him to be a Gryffindor maybe? Or even a Ravenclaw, going by the quiet, learned things we've come to know Derek is into. Books and languages and stuff, you know? But then I think about what he know about young Derek and how, when he was sorted, he wouldn't have been the Derek we know and love. He'd have been like Cedric Diggory, if perhaps a little more of a douche. A friendly, likable douche. I don't think the other traits, the ones that might make him look like a Ravenclaw or a Gryffindor, really developed until after the fire. So I guess I could go a few different directions on him but, when it comes down to it, I'd probably put him in Hufflepuff myself. And then the fire happens and he's not really a Hufflepuff anymore, but people don't get re-sorted.
So, yeah, Hufflepuff!Derek seems right to me, but it's probably not a hill I'd die on, lol. It doesn't jar me right out of the story as much as Stiles being anywhere but Slytherin does.