My wife and me were facing a similar conundrum with our belated honeymoon next month. Stay in the two Sheratons outside of the city (Florence and Rome) or pay more to stay in the city in nicer digs.

The two Westin Excelsiors win out for us (possibly Eden in Rome, last minute decision on that one). The fact is that while you can take a shuttle into the city, if your intent is to visit the city, it's not the most convenient means. Convenience wins out on that one for us. Also, reading some fairly recent reviews on TripAdvisor tended to steer me away from the Sheraton Firenze, although I have heard some good about it as well, from a friend too.

The same can be said for the Sheraton Roma, although if I were to stay at a lower-grade hotel in Rome, not central, I'd go with the Hilton Cavalieri. The rooms there are huge.

Cheers,

Adrian