I think (going bt stereotypes! which the Houses pretty much are) both Gryffindor and Slytherin would tend to be pretty conservative. Classist conservative would be the Slytherins and populist-conservative/conservative-chic would be the Gryffindors. Both of them seem to have radical types of opposite origins.

I think if there's any progressist thought of the pacifist or rationalist or even anarchist kind it's more likely to come from the Ravenclaws or the Hufflepuffs.