Having just done the classics application course (like Laura I have a 3A offer from Trinity), here's what I found:
Trinity - for me, seemed a great college for classics. the Dos - hopkinson - is very committed, but a nice guy. very rich, they'll give travel bursaries and some book bursaries. hopkinson also does a reading tour to the lakes during the easter holidays. in terms of competition, they generally take 8-10 people, with approx. 12-14 applying. their subscription rate is no greater than the other colleges: the cambridge average for classics is 2:1 offers. the academic standard means that you'll only get 3A or - if very unlucky - 4A offers.
kings - a v liberal college as everyone knows. for classics, they won't discriminate against private schools, however simon goldhill - dos - seems to have a preference for (attractive) female undergraduates. i believe last year there were 7 girls and 1 boy. he also likes jewish people as i understand, so if you are and you're considering applying there mention it on your ucas.
pembroke - quite good for classics. dos is scary at first but, by all accounts, a 'sweetheart'. v good for linguistics/philology so if your interest lies here then this is a good college to go for.
downing - very academic college, lots of lawyers. the classics dos, paul millett, has hair down to his waist - it's better you know that before you meet him - he's very highly regarded, and expects a lot from his undergraduates. beware though, downing is tough to get into. this year in particular quite a few people applied - including a good friend of mine - who didn't get in. next year numbers may go down.
those are the ones i know something about. if you're looking to go to a less highly subscribed college i'd recommend robinson - it's good academically, has quite nice accomodation (inside) but is treated snobishly because of its situation, looks and youth.
in terms of general tips, as someone else pointed out classics tends to be self-selecting. certain dons - particularly at richer colleges - won't have to fill their quota, so don't think that just because the competition's less than other subjects you'll definitely get in. on the other hand, use it to your advantage, do lots of reading around and try and make sure they can't discount you. if you can try and meet one of your interviewers before, so you know what they'll be like, and it won't be so nerving. if you can go to bryanston (it may be too late to apply this year, but plan to apply next year), especially if you're taking a gap year. if you are doing a gap year, they like you to have some plan to keep up classical reading - for instance reading 30 minutes a day of latin or greek to keep yourself ticking over.