Papa Carlo's has a very comfortable apartment in just about the perfect location. He and his team are great communicators, and can help you with anything you could need. I can't speak to ease of metro or bus access from the airport because I opted to take advantage of the available car service -- which was about as easy as it could possibly be.
Everything you could need in terms of food and drink are just steps from your door, and if you have the inclination and adequate mobility there really aren't any sites you can't walk to (I walked without trouble to as far as the Vatican on the west, through Trastevere to the southwest, past the Colosseum to Basilican di San Clemente to the southeast, and the Spanish Steps to the northeast).
The only real negative is that the walls are thin, and you are in a very busy neighborhood, so you can hear the neighbors and a lot of street noise. Something to keep in mind if you're a light sleeper.
I would give 4.5 stars if I could, because I think the location is worth the trade-off with the noise, but that's not an option, and I did want to reflect that there is a trade to be made.