Architecture at Cambridge

There is no "best college" academically, as lectures etc are centrally arranged by the department and you can have supervisions at any college in principle. Also for a course like architecture which is both very small and where a lot of the time will be spent in studio, I imagine it's probably a little more department centric than a lot of courses at Cambridge. For college choice it's really just whichever one you like the feel of (which offers architecture - not all colleges offer it!) and keeping in mind that there's usually about a 1/5 to 1/4 chance you'll end up at another college through the pooling system anyway (so don't set your hopes and dreams on one college, just pick one that seems like it would be a good fit for you if you are successful and aren't pooled!).

In terms of A-levels, I don't think maths is an absolute requirement for most colleges, although I gather there is a bit of maths in the course (perhaps a bit more than other architecture degrees, despite it being a fairly art-y course otherwise I gather). So at the very least you may need to prepare yourself for the possibility of some mathematical work. Some colleges do look for A-level Maths I believe (this is outlined on the admissions page - there should be a pdf which shows the per-college requirements) so obviously you will want to cross those off your shortlist for choosing a college

Otherwise taking art and two traditionally academic A-level subjects would probably be the best preparation - these could be essay based subjects like English, sociology, RS, history, politics, etc, or more analytical subjects like maths/the sciences. Some subjects have a bit of both sides like economics and psychology. It would probably be best to avoid applied/vocational subjects, and for Cambridge specifically it might be better to focus on those traditionally academic subjects rather than additional art/design based subjects (although bear in mind other architecture courses may be much happier to see you taking things like DT, textiles, photography etc alongside art).