We loved our stay in Sonja's aparment. She warmly greeted us as we arrived and explained apartment details. It is modern, and extremely clean. The apartment has all the amenities, quiet bedrooms (they are facing the back side of the building), and is in a few walking minutes distance from metro, taxi parking, and Vatican. The area looked very safe, we had no problems walkeing around late at night.
Proximity to Vatican lets you to beat the crowd in visiting the St. Peter's cathedral - that is if you can wake up and be there by 7 am :)
We would definitely recommend Sonja's apartment, it is exceptional!