Marina's Apartment is a top choice - I would always come again: Top Location - less than 5 min Walking from Evangelismos Metro Station (direct Metro to Airport, 2 stations to Monastiraki). Upscale and truely nice neighborhood with lots of nice stores, Restaurants and bars and Close to Lykavettos hill for great Athens sunsets.
The appartment itself is truely nice and very well furnished. Absolutely quiet at night and day. The only (very minor) drawback is that it gets day light from an inner courtyard so you don't have any view.
Everything went very well with receiving the keys. While checking out you just leave the keys in the apartment