I was in a similar position and chose Bristol.
My main reasons were because of the city and because of the law school. Bristol is a brilliant and vibrant city with so much to do, by comparison Warwick is really quite small and secluded, the nearest place is Coventry and let's be honest - who really wants to spend any time in Coventry?
In terms of the law schools, both are great, but I felt that Warwick's law school was very much regarded as secondary compared to other departments like Maths and Business. At Bristol the law school is in one of the must poignant buildings in the city and very much feels like the pinnacle of the university. It makes you feel like your department is one of the main focuses and prides of the university which is something I really value.
Both are great universities at the end of the day with excellent prospects, however I think Bristol is the better choice.