Hi anonymous,
Firstly, congratulations on receiving both of your offers!
I appreciate you've now got a tough decision to make, and you're doing the right thing in trying to research and compare your different choices. I'm a current University of Exeter student (although I study at the Penryn Campus in Cornwall), and I shared some of the same concerns about stereotypes and not fitting in before I started. For context, I'm originally from a state school background from the West Midlands and would never describe myself as being "posh".
Since actually studying as a student here I've found the university student body to be much more diverse than I expected, not just within the UK but also internationally as well. I think that is one of the really great things about university is the range of different people you'll meet, with different backgrounds and perspectives. Regardless of background or socioeconomics I found almost everyone I met to be incredibly friendly and welcoming, and I was surprised at just how easy it was to make friends. Between your course, different sports clubs and societies it's really easy to find like-minded people who share the same interests as you do.
Although I study at the Penryn Campus in Cornwall, I've been to the Streatham Campus lots of times over my degree with work as a Student Ambassador or to visit friends. Exeter, although smaller than large cities like London or Manchester, does have a wide range of nightlife and something for everyone - including not only nightclubs, but also cocktail bars, more old-fashioned pubs, theatres, board game cafes, music venues and lots more. You're also not far from Bristol if you wanted a bigger weekend out or to go and see bigger bands. Certainly if you want to be out clubbing every night of the week until gone 5am then it's probably not the right choice for you, but it definitely still has enough going on as a vibrant student town with over 20'000 students.
If you want some actual data on this topic, the Times do a great job of collating information on this as part of their annual league table - which you can explore
here. If you search under the 'Social Inclusion' drop down menu, you can compare universities on different metrics - such as % of ethnic minority students, or % of state school admissions (perhaps a crude proxy for what you describe as being "posh" or not). For example, 16% of Exeter students belong to ethnic minorities, which is comparable to other universities like York and Newcastle, but less diverse than Nottingham where the figure is 36%. Ultimately which course and university is the right choice for you will be a personal decision, but at least this might give you the information to make sure you're well informed to make it.
In your position, I'd recommend you to try and visit each university at their offer-holder open days, if you're able to. I know for Exeter they should be taking place over the next few weeks and you should've received information about this via email shortly after your formal offer. When I was in your shoes looking at different universities I found that actually visiting them, talking to academics and current students, and getting a feel for the nearby town/city (including the nightclubs and bars if that's important to you!), was the best way to really get an understanding of if that university was the right choice for me.
I hope that's helpful, but please get in touch if you have any further questions I can help with.
Kingsley
University of Exeter Student Ambassador