At UCL, we have 4 courses each term. Of these, we get 3 hours of lectures per course, one hour of 'problem classes' per course (although, I haven't had one of these yet) and one hour of 'help classes'.
We also get assigned two tutors - one applied, one pure - who we have an hour of contact time with per week in a small group (between 4 and 6), which are quite helpful, for checking over any arguments in your proofs you're unsure about and 'tightening the screws' on any proofs, if you will.
We also have a 'mentor class' with a second year student for one hour per week, which in, again, we go over any homeworks/do some maths for fun, this is in groups of 12 to 15.
UCL also offers a quite generous bursary to all students (half of your maintenance grant), and all of the accomodation is easily within walking range. It takes me 4 minutes to get to the maths dept. from where I'm staying (although, we don't actually have any lectures in there).
Personally, with offers from both last year, I chose UCL due to, well, it being in London. I couldn't find any other differences.