Having interviewed at both schools I would definitely go with USF. While I was impressed with FIU's goals and plans for the future, and I know USF is not a national power house med school, I still think something has to be said for going to a med school that has been established for 35+ years as opposed to 0 years. Also, outside of one floor, FIU didn't really have any sort of medical campus when I interviewed they just took us around the undergrad campus. However, I'm thinking since I interviewed last october they probably have some new facilities up/under construction by now?
If cost was about equal I would say USF. But, reasonably, money does make a difference.