I don't know too much about Warwick, been there once. The campus is flat and nice to walk in, feels quite secure and pretty.
I do live in Exeter and it's a nice city, lots of shops when you go out, however it's quite hilly and the slopes are rather steep (you'll be very fit after these few years haha!) It's a relatively safe city (if you avoid shady areas and have common sense ofc)
Most of all, look at the course content and coursework, teaching methods etc, or go to an offer holder's day to see which city you like better!