I think that the house doesnt really matter in the end. I mean Slytherins are more proned to be dark wizards and Gryffindors are more likely to fight these dark wizards but it really just depends upon the certain case. I mean ive made up a few characters in Slytherin, one case is the father of my characters Aron and Brasce Matthius. Hes a really powerful wizard that transforms into a good guy and does Dumbledore a service against Voldemort. Yet his son Brasce joins Voldemort because hes a coward inside and kills his twin sister.....but it really depends upon the person in my opinion.