Well, my answer has been and remains (a) all of them, with the proviso that I have no insight into colleges outside of the US; but (b) with a caveat that the built environment—including the existence of dorms and such—can make it more likely that such conversations can occur, simply because students are more likely to be in more frequent contact with each other.
If my (b) is correct, then that would explain the perception that, say, community colleges are less likely to have intellectual conversations than selective liberal arts colleges—it isn’t that the students are different, but rather that the students are around each other less.