In terms of how best to look at colleges, I think what I did might make sense. It's hard to spend a lot of time in Cambridge, so if you're only doing a day trip (which of course you really should before you consider applying), rather than doing college open days go preferably during term time, or during the summer when all the international students paying for a summer holiday at Cambridge turn up.
I went on the alternative prospectus from CUSU (far better than the university one for finding out about colleges), with the requirements that I wanted to stumble out of bed to the history department, that I wanted music practice rooms, and a decent priced pint. You may have different or similar requirements. I narrowed it down to six, in August I emailed the admissions tutors to see if any could see me. All the colleges invited me to look round unaccompanied, Queens and Kings met me for a quick discussion, and really it was just falling in love with Kings once I'd had a look round that did it for me.
So that's what I'd recommend. Make a shortlist, spend a day walking round Cambridge, and then decide from there.