In Bristol you will have fun, and in Warwick you might have slightly better job prospects… Warwick literally sounds like the most boring place on earth, whereas as a first year at maths student at bristol I can confirm that it’s very very sociable and there’s a lot of cool people around. The maths course can be challenging but they have a lot of academic support and if you’re smart then it’ll be no problem whatsoever. I had a similar choice to make and have absolutely no regrets about going to Bristol, so I do recommend.
Basically bristol is a cool city and still a great uni whereas warwick is a boring campus uni with a slightly more prestigious maths course