Sweet's place in Trastevere is a great option and we were happy to be there for our first stop in Rome! The location is excellent - really right in the middle of a great neighborhood with all kinds of cool restaurants, shopping and bustling activity well into the night. It's also a short walk to the central area of the city. The apartment is cozy and despite the proximity to activity, was quiet in the bedroom as other reviewers have mentioned.
The only reason this is not a 5 star review is that this place is really quite small - to call it cozy would be sugar coating it. The ceiling is low in various places, but the worst is the bathroom. I'm not super tall (5'7") but I had to duck my head while using the toilet or brushing my teeth. And the shower is a problem - with just a curtain separating it from the rest of the bathroom. The first few showers we got water all over the floor. Finally we figured out the trick - put the bottom of the curtain IN the water at the bottom of the shower so it gets wet and heavy and stays put.
Overall, this was a solid place to use as a base for a few nights, but visitors should be aware that you are paying mainly for the prime location and the space is about as small as two people can possibly inhabit. The pictures do a good job of making it look bigger than it is!