I was just browsing and ended up looking at this thread...
The whole media hype around crime in Nottingham's rubbish, it's the same for more or less any city, everywhere has its rough parts. If you're getting into things like that the area around King's college isn't any better, don't know what Cardiff's like...
I know I picked Nottingham for a different course, but they're a fantastic innovative uni with a beautiful campus and who are consistently rated well, one of the reasons I applied in the first place.
Have you visited both cardiff and notts? Go for where you felt most at home.