We stayed at the Domus Romana which was walking distance to most major sites- Colosseum, Spanish Steps, Trevi Fountain and to the railway station as well as close to an underground railway stop. The restauraunt across the road was nice and the immediate area not too touristy. There was a gelateria just down the road. It's marketed as a 4* but I'm not sure it quite qualifes as one. Nice hotel anyway. I don't know what it would cost though (I booked it in a bundle with flights) and it isn't in a chain so no points.
The general advice (which strikes me as sound) it to avoid the area immediately around Termini station because it's quite rough at night - there's certainly plenty of pushy restauraunteers at all hours.