I'm a first year at P&S and live in Bard Hall. Most first years do choose to live in Bard Hall, but it is by no means required. Some students choose to live off-campus either in apartments in Washington Heights, near the Columbia Undergraduate campus (116th and Broadway), or on the Upper West Side. Although Bard isn't the most luxurious place in Manhattan, it is a great first year experience. Its really close to classes and all of the Medical Center facilities. The rooms are fair sized and many (including mine) have great views of the Hudson. It's cheap, the gym (squash courts, swimming pool etc.) is downstairs, there is a dark room, and a well utilized study lounge.
More importantly it is a unique opportunity to interact with your classmates in a way that few other schools provide. In a large and sometimes daunting city it's nice to have the comraderie and support of your fellow first year classmates surrounding you. That being said, if you are married or really need your own kitchen, or a private bathroom, Bard Hall is not for you. I really enjoyed my experience in Bard Hall and would recommend it to most incoming first year students.
I see you are still debating between a few schools and hope that you are coming to our revisit weekend. You can't make the wrong choice as far as medical education is concerned so where you will be happiest will ultimately guide you decision.