Or this:
http://extras.timesonline.co.uk/tol_gug/gooduniversityguide.php?AC_sub=Architecture&x=38&y=4&sub=It doesnt look like Uni of Notts is on the list for architecture, but UCL is #1 for their research quality. I'll be doing Chemistry research, and UofN is ranked 13th, but for their quality research it's second--rated at 3.9 (ahead of oxford).
Both are good schools (from what I know), so it seems to come down to what you're most interested in doing. You'll have to look at what experiences you have, and which you most want to develop. Also, which would be more recognised in the US? Which has better job prospects/opportunities within the course to have an internship?
A friend of mine studied at UofN for her master's in art history. She absolutely loved it. For her it was about the atmosphere/the campus is nice, old, and lots of green/and she felt like her department really cared about her and her success. I've been to several open houses for UCL (different departments), and I too, Love! London. So it might be hard to pass up. But in terms of the programs, they didn't really excite me.. It is expensive, but if you think you'd be happier in London, then maybe the expense is worth it? I dont know, you're already taking out student loans, right?
but, you can always move to London after completing your MArch at nottingham. That's pretty much the plan for me and DB.