Ok, so there seems to be a definate lack of dental students bigging up the Bristol here!
I had the same problem choosing between the two, but at my interview I was seriously looked after at Bristol - the lecturers and older students really made a huge effort to get to know you.
In terms of course, Bristol is going through a major overhaul, the entire Dental Hospital is being refurbished and is majorly brand new! Very cool, and we are getting to see patients very early now, which is awesome!
In terms of city, Bristol is of course much smaller than London. 1 in 8 people in central Bristol will be a student! You are always bumping into people you know, and the best bit is that everything is in walking distance, or a short bus, so that you feel very close to the city!
And finally social scene is immense - everywhere is geared up for students if you look for it! Very cheap nights out can be had!
Hope this helps! Big up the Brizzle!