Best Colleges for Geography at Cambridge UniversityWatch this thread
And the college pros and cons section of TSR's Cambridge info:
All colleges have (largely) the same facilities, collegiate atmosphere, fantastic tutors and friendly students, so choosing your college is not the biggie you probably think it is. Bet if you do get some students/graduates here, they will tell you how great their own college is! It's like having your own family.
The important thing is getting into Cambridge. I don't have a Cambridge demystified geography chapter, but I do have one for Oxford: