It's worth pointing out that if you want self-catered, you don't share at Cuth's, that's only a possibility if you live on the bailey as that's the only area that rooms are shared at.
As for which college you choose, depends what's important to you really, whether you are the type to go out drinking or just the type to sit around and not. While every college has every kind of person, some have more of each type than others. If you want to be around locals, I believe Cuth's - for whatever reason - has the largest number of them. Other colleges will have the best bar (well actually, that's Cuth's too to be fair.. :P), the best gym and sports facilities, the best catered food.. and so on.