Our stay at I Coronari was magnificent. The location is an easy walk to St. Peter's, The Pantheon, Trevi Fountain, and literally two minutes walk to the Tiber River and Castel Sant'Angelo. It is also a very short walk to a main bus route to the Colosseum, Forum, the Capitoline Museum, and Palatine Hill. The walk to the Borghese and the Spanish Steps is a bit longer, but very doable, and the sights along the way are stunning. There's a small supermarket nearby on Via Coronari where we could get basic breakfast food and good wine.
Mario was waiting to greet us when we arrived and provided excellent recommendations for dinners. He was available by phone if any problems came up (zero problems while we were there), and he arranged a cab to pick us up at 6 AM on the day we departed.

We stayed in 3 other Air BnBs on our trip (Venice, Cinque Terre, Florence), and we were very happy with all of them, but Mario's apartment was the best.