My girlfriend and I had the most wonderful stay at the la Casa del Cinque. The interior is extremely well decorated and you feel like you live in a restoration hardware catalog. Checking in was very simple and the apartment has all the necessary resources available for a tourist in this gorgeous city (guide books, cooking books, recommendations, Internet, etc.)...
The balcony has amazing views on the Trastevere and the western side of the city. the street on which the flat is located is lively and has plenty of food/drinks options.
I would highly recommend staying in this apartment as it is very well located and it feels like the best version of home possible.