We had a very nice four night stay at Simone's place near the Vatican. We came in from Florence via the train, and the apartment was a convenient three-minute walk from the San Pietro rail station. We also used this station to get to the airport, which was easy.
The apartment itself is very spacious and has all basic amenities for your needs. It's on the 5th floor, but luckily there is a lift so no need to worry about hauling up luggage. The gem is of course the rooftop terrace, which has a great view of the Vatican. We enjoyed our time on the terrace at night.
The only issue we had with the place was that the bedroom A/C unit was not working so we had to sleep on the pullout couch in the living room, where we could utilize the kitchen A/C. It would be nice to get the bedroom A/C working.