This is a fantastic place. Huge ceilings! One flight of stairs up and it comes with an elevator. It is a block from the nightlife of Trastevere and the bedrooms face the street but it never caused us problems--it might for some. Trastevere is a sweet, walkable, and lively place with its charming shops and restaurants. it's maybe a 10 minutes walk to the Campo de Fiori. There's a tram that's somewhat nearby that will take you to the Piazza Venezia in about 5 minutes too.
What sets this apart is the prompt service we received. We were late arriving in Rome and Valentina, who was to meet us, was extremely considerate about our issue and was waiting for us. We requested a second set of keys and she brought them over the same morning. If we lacked anything (we didn't) she requested that we tell her instead of buying a gadget or cooking utensil. She checked in to see how our trip was going as well; it was quite different than other places we have stayed and we really appreciated that.
If you stay here and have a stroller aged child, make sure that your stroller is ready to take on the cobblestones! we brought a cheap stroller and about 2 hours into Rome we knew we needed a new one.
The Metro is quite a ways away from Trastevere so you'll have to combine the Tram and the bus system if you don't like walking.
Perfect location for us. Lovely area. Have already recommended it to friends.