I've been in York, and studied at the University of York. And, I'm heading back to the city, not the University sadly. It may not be London, but I had a wonderful time there. The people are great! I met quite a few friends that I have managed to keep (going on a year and a half later). Also, I have a good friend who was in the Medieval Studies program, who loved it, and felt he received an excellent education there. There are quite a few ways to meet people on the campus too (or at least that's what I found). However, I do not know anything about Queen Mary, so sorry I can't make any comparisons.