Just graduated from Warwick Business School in Management. If you have any questions, feel free to ask. I would recommend Warwick for pretty much all the reasons already stated. We have a brand new business school (built 2 years ago) which was a luxury to attend for my final 2 years.
Regarding the social life, I've always maintained the belief that if you can't make a social network with 6,000 freshers, then it's not the geography of the university that's the issue. It's you. That said, WBS, and Warwick university in general, is fairly tough-going, and so it attracts people who treat university less like an adult summer camp, and more like a competitive intellectual feat. Like every university though, it's an instituion that caters for 18 to 23 year olds, and so we have about 5 clubs that are fairly active. The student union holds you for the first month or two of freshers, and then you'll be bussing it to Leamington Spa (20 mins) for Smack/Neon, Coventry (20 mins) for Kasbah, or Birmingham (20/30mins) for Gatecrasher.
Given that your university sets you up for the rest of your adult life, I'd discourage choosing one on the basis of the four walls that you'll be drinking in.
Good luck