I second the comment that it depends on what you like. I'm not that into art but found the Uffizi in Florence to be memorable. And the statute of David is breathtaking. Florence is also the home to some fabulous leather goods if you like that. We stayed near the Ponte Vechhio and walked everywhere in Florence, which was nice.

I spent less time in Rome, but I'm a big history buff, so it was thrilling to see some of the ancient Roman sites and I'd definitely go back to Rome if I had to choose between that and Florence. For me, there was much more to do and see in Rome. I could have spent several days just walking around the ancient Roman sites. Vatican City also looked really interesting and there were a number of museums that I didn't get to but they sounded fascinating. There is also a ton of shopping, although some of it is very expensive. Rome definitely felt bigger and more hectic than Florence to me.

All things considered, I'd suggest the OP choose Florence and try to include a trip to at least one other site in Tuscany.

Florence!!!! I love Rome, but Florence is magical. Just sit outside in of the cafe's with a bottle of wine, and watch the world go by. Oh how i miss it.