I dont know anything about the law courses unfortunately, but i feel i have to put a word in for oxford here! i'm not actually at oxford yet, but hopefully will be next year, obviously if i get the grades...
both Christ Church and st. johns are fab, i have an offer from christ church and i spent a bit of time at st. johns whilst i was in oxford for my interview as a mate applied there... the room i saw at st johns was really nice, and the gardens are gorgeous... christ church is like everyone says, big and impressive. The reputations of the colleges seem to be that st. johns is rich, so you get cheaper rent, book grants etc and that folks there work hard. The christ church reputation seems to be that it is a bit too full of rahs (have you read brideshead revisited??)... but im not too sure about that, im taking that with a pinch of salt. The thing that got me about christ church was all the tourists, but i like tourists (being a crazy one myself).