The glib thing to say would be that the main difference among them regarding social atmosphere is that Yale and Princeton have social atmosphere. That’s really not justified, but there’s little question that the portion of people’s time and enthusiasm devoted to social life at Yale and Princeton is somewhat greater than at Chicago. Princeton has its eating clubs, which many people who aren’t Princeton alums find creepy, and which Princeton alums generally love (even those who didn’t join one). Yale has something like 50 senior societies, and all sorts of underclass clubs, established and ad hoc; Chicago has . . . I don’t know, nothing really equivalent to that. Some weak frats that most people don’t join, but don’t mind either. Chicago had a residential house system before Yale developed its residential colleges, but Yale’s residential colleges work about 100x better (and cost not far from 100x more). People at Yale are fiercely devoted to their residential colleges years after graduation; I don’t think there are many Chicago students give a crap about their house after the middle of their second year. (In that, they are similar to Princeton students, except the Princeton students have their eating clubs.)
Yale and Princeton are very, very Eastern Establishment oriented. New York and Washington. Chicago has plenty of connections both places, but feels more Ivory Tower-ish, and of course more midwestern.
In reality, all three resemble one another a lot more than they are different. Yale and Chicago are really very, very similar, except for the residential colleges, the virtual torrent of student art of all kinds at Yale (vs. a perfectly normal amount at Chicago), Yale’s smug sense of privilege, and its much more grandiose version of fake Gothic architecture.
Here are two major differences, and at the end of the day they probably determine where you want to go:
First, their environments are very different. Princeton: a defined, set-off campus in a rich ex-urb, a showplace for landscape architecture. Yale: dominates the center of a small, somewhat gritty New England city (and while its college is about the same size as Princeton’s or Chicago’s, as a university it and Chicago are both much bigger than Princeton). Chicago: dominates a sleepy, leafy, well-to-do enclave miles from the center of one of the greatest cities on Earth. And that, by the way, is one of the reasons college-specific social life is weaker at Chicago – at Yale and Princeton, everything worth doing is on campus, with maybe a weekend trip to NYC once or twice a semester, while at Chicago you are on the public transportation grid of fabulosity.
Second: Maroon looks good on lots of people. Navy and white – sounds good in theory, but it’s a little tough to pull off in practice (navy and grey versions are much easier to wear). Orange and black? No wonder Princeton students stick close to campus . . .