I get my exam results tomorrow to find out if I get in for definite, so I'm not at St. Hilda's yet! (I'm faaaaaairly certain I'll get the grades though!) But I've spent four days there during the interview process, and been to an induction day a few months ago as well.
If you're into music, I think St. Hilda's is great. They've got this new music building in the college itself called the Jacqueline du Pré building that has several practice rooms with pianos that any St. Hilda's student can use for free. So I think it's quite good for musicians, especially pianists. I play the piano myself, and this facility is one of the things that attracted me to the college. Here's a link to their website where they talk about music at St. Hilda's:
http://www.st-hildas.ox.ac.uk/student-life/student-life-music-st-hildasAlso, I'm not 100% certain, but I'm fairly sure that societies are across all colleges, and not in-college. I might be wrong about this, but I think you can join a society no matter what college you are in.
Obviously I can't give you a complete answer since I'm not actually at St. Hilda's yet, but from what I've experienced, St. Hilda's has a very nice atmosphere. It seems to be a very friendly environment, and I personally enjoyed that and applied there because of it - they were the friendliest college I visited. Also, there is a good amount of state school students applying there, and a good balance between boys and girls. I can't speak for their attitudes towards academics, but I'm sure they work just as hard as every other Oxford college. And the plus side is it's really pretty! There's a river on site and in summer students can use the punts for free.
To be honest, I think everyone who goes to Oxford is going to have a chance to get as much out of their degree as possible; that's more up to the individual than what college they attend. It's Oxford, so standards are going to be high across the board.
What subject are you thinking of applying for?