The Hilton Cavalieri in Rome, indeed. Very upscale, and as a Gold, was put on the exec floor with access to the best Hilton lounge on the planet. Rooms are exquisite, even if you don't get a city view room (as I didn't). Location is a 12-euro cab ride from the "city" but they have a free hourly shuttle both ways.
I also liked the Buenos Aires Hilton--it's only a 5-yr old hotel with a great lounge and a quick cab ride to the city's hot spots. Nice rooms. Beautiful pool area 6 stories high with nice views of the city. Great concierge staff.