Simone's place was clean, on a quiet street in Testaccio. If you are looking to stay slightly away from the noise and hustle of the main sights (but still 20 minutes walking from most of them), Testaccio is an excellent choice! Simone's place is also very close to Trastevere, so the scene there is easily accessible.
As for the apartment, it was lovely. Nothing to complain about, and it was as described.