We stayed in an apartment for 4 days in February. The flat is well located between Roma Norte and Condesa, two very cool residential areas with loads of great restaurants, cafe's and bars.
Its close to the subway, and is only a few stops into the Centro Historico where some of the main sights are. The flat itself is self contained, brand new, and nicely decorated.
Our window did look out onto the main street, though as we were out exploring all day this didn't affect us much.
Leslie was an excellent host, and was on hand to help with any problems or questions with a prompt and friendly response. We'd definitely recommend it!