We had a wonderful stay at San Peter House. The rooms are big, the house is clean, the welcoming by Daniela and Frabrizio is perfect and the apartment seems brand new.
The location is great if you want to be close to Vatican and not far from Campo di Fiori. The great thing is that you're in a pretty quiet street for Rome so you can sleep wonderfully with the windows open without too much noise.
We were 4 in the apartment and using 3 rooms, but it can easily accommodate 6 adults and 1 or 2 children. We will recommend the place to our friends.