Adora: Gryffindor. I am a huge fan of Harry Potter and I hate the whole "good guy = gryffindor, bad guy = slytherin" thing, but Adora is a perfect Gryffindor. I can kinda see Adora as a Slytherin, as Noelle said, but Adora is more brave than she is cunning.
Catra: Slytherin. Once again, not because "good guy = gryffindor, bad guy = slytherin", Catra is just a perfect Slytherin. Catra is definitely ambitious, despite what Shadow Weaver might say. Catra is also cunning and resourceful. I mean, just watch the episodes where Catra is in the Crimson Waste, and that should be enough evidence. I tried to see Catra as a Hufflepuff, as Noelle said, but it seems like the worst fit. Catra is certainly hard working. As for loyalty, Catra is loyal, but her loyalty is wavering. Throughout the show, we learn that her true loyalty was not with the Horde, and it seems that her loyalty was to Adora. However, I would argue that if she was loyal enough for it to override her cunning and ambition for her to be in Hufflepuff, she would have had to be loyal enough to leave the Horde with Adora. And she has no other real loyalty to any other character. I wouldn't say that Catra is patient and she is certainly not a fair person.