Hi, you made a really good choice by choosing the bailey - u'll be in the city right next to St Chads, St Cuths and Hatfield on a lovely cobbled street (although I did see one student slip and fall and drop all her stuff - no injuries, just humiliation!), but you will also be a stones throw away from the river and some gorgeous woodland.
I'm not too sure about the social life at St Johns, however, the college bar is almost definately going to bustling on many nights. If it isn't you have a number of pubs (colpitz - pub quiz on tuesday - more fun than it sounds), clubs (warehouse etc), other college bars and of course the SU functions (planet of sound).
You probably will not be living in the college accomodation for the whole course. In second year, you will most probably live out with a group of friends in rented accomadation and in the third year you get to choose, but most people choose college accomodation.