I highly recommend Aris' Airbnb.
The flat: It is in a great location, close to a metro station as well as a grocery store and many restaurants. The flat was large, modern, and clean. The air conditioning and Netflix felt like such a luxury after long days of walking through Athens.
The communication: What we enjoyed the most was Aris' hospitality. He went out of his way to help us. He picked us up from the metro station, gave us lots of touristic advice both before our trip and the day we arrived, offered to organize a bus trip to Poseidon's Temple, and checked in with us via email during our stay.
Overall my three friends and I can all highly recommend this Airbnb and if we return to Athens in the future, this would be the first place we'd check for vacancy.