OK. I am going on second year of mathematics on QMUL. In my first year I had first and I have friends that study in different universities. I can assure you that if you like challenge then mathematics degree is good for you no matter what university you go. You must be ready for a huge jump from A level I had A* to degree level. On QMUL you have support. PASS and academic advisor are really helpful. You can't imagine how many people from first year gone searching help in very first months of the course. If you will come searching for helpful hand it's likely that you will meet me there. QMUL is good. I am happy with my choice.
Best of luck