I thoroughly enjoyed my time at Cardiff University. The campus is vast, so there are many buildings that you can use to study in. The facilities for computer science are excellent.
A slight downside is that some buildings are advertised as having 24-hour access so you can study anytime, but that is only sometimes the case. I had some trouble accessing some 24-hour buildings.
I would definitely recommend Cardiff University. It is a great place to study, and everyone is very friendly.