*Balliol (great bar; JCR pantry; relaxed atmosphere; centrally located and near supermarkets)
*New (fairly large in numbers; you can walk on most of the lawns; 90% of students have en-suites; one of the most beautiful bars in Oxford with several 'rooms' on different levels, regular quiz nights, a big screen, free pizza/ice cream/ other nice food nights, sofas, a pool table, & arcade games; excellent bops; common room with plasma screen, sofas, Sky TV, computers/printers, daily newspapers, a chocolate machine, giant jenga and another pool table; a lavish white-tie ball every three years; thriving music and sports scenes)
*St Catherine's (largest undergrad college; very friendly and sociable; cheap college bar with entertainment, serves snacks during the day; Sky TV in the JCR, with DVD player and newly installed sound system; private dining room for hire with a TV so you can have your own mini cinema for a night; good facilities; 3 computer rooms; relaxed atmosphere; about halfway down the Norrington Table)
*St Edmund Hall (fairly central; 'party college' with great bops and the biggest dancefloor in Oxford apparently; the bar actually looks like a pub; friendly atmosphere; near the bottom of the Norrington Table)
*St Peter's (right in the middle of Oxford; extremely sociable; very active JCR with regular entertainment events; JCR has leather sofas, a free foosball table, ping-pong table, quiz machine, pool table and arcade machines; near loads of eateries as well as Odeon and 2 theatre houses; close to Oxford coach station, 2 taxi ranks and all the major bus stops on the High Street; very new bar; near the bottom of the Norrington Table)
*Wadham (central position close to Turl St; inclusive reputation; on-campus pub; great common room with arcade games, Sky TV, sandwich bar, a pool table and giant leather sofas; student plays in the theatre every week; fortnightly bops; free all-day music festival called Wadstock; only college with a mixed JCR and MCRL friendly and relaxed atmosphere; about halfway down the Norrington Table)
I don't actually go to Oxford - these are taken from the Oxford College pros and cons page on TSR. Hope it helps
Tbh most colleges will have a good social scene and a lot of them are handily located!