That’s understandable. But Penn is a big enough university that I bet you would find plenty of potential friends who you are comfortable with. And there is no guarantee that UChicago or any other university would be less snobbish or cliquey. UChicago has quite a few private high school students that could be perceived as snobby, and not that it is necessarily a bad thing, but some UChicago students and alumni can be pretty pretentious. They are smart and very well educated, but most importantly, they want you to know it.
And a university’s social culture is such a subjective topic, the second or third hand opinions you have encountered may or may not be similar to what you would actually experience.
I have no connection to any of these specific universities, but I just want to highlight for you that I think you should stick to the objective facts, and weigh your options based on what you know to be true: the specific academic offerings that fit you, the logistics of fitting the core curriculum into your remaining years of college etc … my advice is don’t base such an important decision on subjective opinions and feelings that may or may not be true.