Hiya,
I haven't personally lived in either yet, but I do know a decent amount about the University of Manchester, since I'm looking at firming them for chemistry (and also information osmosis from searching about it and talking to people), but do take everything I say with a pinch of salt anyways.
I'm going to go out on a limb and say realistically, you won't notice much difference in the size of the cities, both are very large cities (especially if you're coming from a village, having suffered through living in my tiny little village long enough, even a small city like Cambridge felt big), and so it's better to consider other factors for it, I personally chose to apply to Manchester over Sheffield (although that's because Manchester has very very good chemistry), consider having a look at how they perform for specific subjects, also bear in mind that entry requirements are only really a vague indicator on how good a course is. A lot of the polytechnics (e.g. MMU, ARU, etc.) still have very good courses, although they have much lower entry requirements.
Another thing to consider is if you want to do a year abroad, Manchester has a frankly dizzying number of destinations, so you'll probably have more luck there than with Sheffield.
In terms of nightlife, I definitely think Manchester will have more (although you don't necessarily need to engage with it), I don't know as much about Sheffield, but in Manchester, there are 3 places for student accommodation: Fallowfield, Victoria Park, and City, where Fallowfield is the 'party campus' and Victoria park and city are quieter, so that's another thing to consider
I'd reckon go to the open days and offer holders' days (especially offer holders' days, the open day at Manchester was honestly a bit pants, but the offer holders' day was amazing) and see the cities for yourself, also bear in mind that if you do feel overwhelmed in Manchester, you can find accommodation slightly out of the way, either in a suburb or a nearby town, the transport in Manchester is
very good compared to most other places, so living in a suburb especially you won't have much trouble commuting in.
I'm also personally going to recommend to go to Manchester, but that's just my own personal opinion, and isn't really substantiated by any hard facts, since which one you prefer is just personal opinion
If you're looking for LGBTQ+ friendly places, Manchester is definitely better known for them, but there are plenty in Sheffield too, I'd recommend looking online, as there are a lot of guides and directories, here's one for
Sheffield, and one for
Manchester (I'm sure residents of them will be able to give better ones), personally, I really liked Manchester, because when I went to the chemistry building, they had all-gender toilets, so I could actually use the bog in piece, I can't say for Sheffield, because in the end, I didn't apply (I switched them out for York, so I wouldn't be applying to 2 places with ABB), but that's something that was nice.
hope this helps and good luck
