My understanding is that from an academic perspective college choice is more relevant at Oxford than at Cambridge. So, at Cambridge, provided your college actually offers your subject, you should be able to have a free choice within the course of topics - if your college doesn't have supervisors it will send you out to one in another college.
At Oxford my understanding is that supervisions (or tutorials as I think they are called there) tend to be more college based and limited to the modules that the Fellows in that college can teach?
Assuming your son is going for Cambridge for architecture, most of the colleges are open to him (apart from Corpus, Homerton, Hughes Hall and St Caths. So I think the things to look at are:
- application stats (for colleges and subject)
www.study.cam.ac.uk/undergraduate/publications/docs/admissionsstatistics2013.pdf
I see that Architecture is one of the hardest things to get in to do! Big caveat is that the stats could be totally different the next year, especially if those applying the following year take last years stats as a bible.
Ones that are further out, e.g. Girton, are going to be easier to get into/. Which college is near the architecture faculty?
Modern colleges tend to be less popular as everyone wants to go to a pretty medieval one. Eg Robinson, Churchill,
It seems to me that even if the smallest college (is it Peterhouse?) and the largest (Trinity) usually offer the same percentage of architecture places each year (thought they probably don't) then that equates to more places at Trinity than at Peterhouse. That said they don't have fixed quotas for subjects to allow them flexibility.
Also, in a big college you have more chance of finding like minded friends. Conversely you don't get that small-community feel.
-Fame/wealth of college
Not sure how this plays really. I know from being at a very wealthy and famous college that there were definite benefits - no clearing out your room every holiday, they weren't all that bothered if you didn't pay a bill, lots of bursary support, generous grants and prizes to toddle off to look at paintings in Venice. I wonder if people are put off applying to the very famous colleges (e.g. Kings/Trinity) and as a result the hardest ones to get into are the ones that are pretty and centrally located but not imposingly famous (e.g. Trinity Hall, Sidney, Emmanuel, Clare and so on)
Colleges do have stereotypical characters, not that they are defining, but sth to think about. In my day it was something like this: King's is very left wing, state school, and progressive, with politically minded students and the abolition of many traditions e.g. formal hall. Trinity is traditionally the "posh" college - while very diverse and not at all "posh" now it does retain traditional customs and I don't think anyone would describe it as a hotbed of political radicalism! St Johns again is big, imposing wealthy and sporty and the butt of "I would rather be at Oxford than St John's" jokes. Jesus is sporty and rugby, Peterhouse is very small and Conservative, Christ's and Caius are are very swotty, and Emma, Sidney, Clare and Trinity Hall are kind of middle of the road normal.
Getting put in the pool is no guarantee of a place, its more of a potential second chance at a place. Basically you get put in the pool if they thought you were good and they think you should get a place somewhere, but they are full at that college. It then is up to undersubscribed colleges to fish you out of the pool if they wish. Must be torture for the kids involved.
At the end of the day you can read the stats and read all the info till the cows come home, most people quickly grow to love the college they go to whichever it is. Your son might decide to apply to the college with the most arch places, but then of course you can bet your life all the other applicants are doing that too.
So I think he should just pick the one he likes best and put his energies into making himself a really good candidate.