I searched extensively for the perfect place to stay in Rome, based on an Italian friend's recommendation that I stay near Piazza Navona or Campo dei Fiori. Because it is an ideal location, it tends to be expensive. However I found Residenza San Pantaleo for about $120/night for two and the reviews were mostly good.
I was highly satisfied with my stay. You must know, though, that this is a residenza, meaning it's not a full-service hotel with a reception area and all. They know when you will arrive and take great care of you at arrival, but there is no one at reception all day. For assistance, you go to a sister location, where Nadia is more than happy to offer any services you may need.
The room was basic but not as cramped as I have found in, say, Paris. They supplied an electric pitcher to boil hot water, some teabags, sugar, and instant coffee. This was a nice perk have for Americans who are used to coffeemakers in the traditional hotel room. There was also a small refrigerator and the ever-important safe. The room was clean, the shower was hot, and there was a working towel warmer. There is free wireless in each room (there may have been computer access, but I don't think it was readily available) so you can access the Internet via your smartphone.
In terms of noise, the window is well insulated. Only when the streets were nearly empty and a lone car would soar down the road (we did not face the main drag, but the building is on that street) would the sound be disturbing, and this was mainly in the very early hours. You could occasionally hear other guests, and the one drawback of not having reception is you could not complain to anyone about a loud TV late at night. I was awakened on more than one occasion by other residents who seemed unconscious of the fact that others were sleeping.
The breakfast a few doors down at Jerry's was very simple -- juice, cappuccino, and a pastry -- but the service was lovely and you could always order more very inexpensively (1 euro for most pastries) or exchange the croissant for something else. My son got a chocolate stick every day instead of the croissant, for example.
Nadia will arrange for you to be picked up at the airport and can arrange for your return as well at a reasonable (and trusted!) price. We arrived very tired at around 9 a.m. and our room was not ready, but the assistant offered us to lie down in another room until our room was ready, which set us right for the rest of the day.
From this location you can walk pretty much everywhere -- Vatican, Colosseum (a little further, but not bad), Trastavere, Spanish Steps, etc. You need to take a bus to get to Termini, but the bus is right in front to take you there. Anyhow, there is not much tourism near Termini. Many restaurants/gellateries nearby. I recommend this location and this hotel very highly and would definitely stay there again.
One thing: the rooms could use a box of tissues (e.g., Kleenex facial tissues). Residenza San Pantaleo is very responsive. so I imagine they will start stocking them immediately after this review is posted.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC