Ah, they did better than Jesus against London Metropolitan then? hehe.
Ellie, what would you like to know about the colleges? Most people on here can tell you objective facts about both the colleges or about the way they're viewed, if any of that helps you.
gzftan made a good point about accommodation: Caius first years live a fair way from college, although it's handily close to the Sidgewick site (place for arts/economics lectures). I happen to know that they have to pay for about £40 of hall meals up front though, meaning that even though they live a long way away from their Hall they have to use it until their meal tickets are spent, or they'll have effectively poured money down the drain - that seems a bit of a pain. Trinity first years live on-site in a modern monstrosity of a building called Wolfson Court; the rooms are pretty big though (and a fair few are ensuite).
If you're at Trinity you get coddled because the college is so rich: you can take out books on loan for the whole year rather than buy them, the food is very nice and reasonably priced and they'll give you money for just about anything you can dream of, especially if it's to do with travel or music. But their college scarf is minging. (Well I had to find something!)
Don't know too much about Caius, except that the people I know there are nice. Oh, and they have a funny traditional race for their economists at the start of the year... don't know if land economists are included in that! (And no, I'm not saying any more - wouldn't want to spoil the surprise for anyone headed there.)
What else? Both Caius and Trinity have beautiful main sites and a few well-known fellows - if you're at Caius you'll see Stephen Hawking quite a lot (which I think is quite cool, sad though I am) and Trinity have the Astronomer Royal for their Master, amongst others. I assume you'll have visited them both, from what you said... I'd suggest you see if you can visit both during term-time as well and just go with the one that feels most right. Can you see yourself living there? That's the really important thing.