i had to make this decision the past few weeks, and it was hard!! i think both are two of among the best schools in the nation. ultimately though, i couldn't really give upenn a fair chance, as much as i wanted to, and as good of a school as it is, because of the costs -- nearly $100k or so higher than ucsf in my estimation. if not for the cost, it would have been much harder. when i got the letter from corky confirming that they received my notice of withdrawal, i almost cried a little inside...lol. it sure sucked to have to give up a upenn offer. upenn was by far the most impressive school in terms of communicating with its applicants.
but maybe even if the costs were similar, i would still have chosen ucsf. their housing options seemed better to me. and i liked the smaller class size. san francisco appealed more to me than philly as well.
hey, did you get the dean's scholarship from upenn? that would so help your decision!!