I would recommend staying at Christos' place if you're going to be in Athens for a few days. Besides transport to and from the airport I traveled around the city by foot and the location of the apartment made this very easy (5 minutes to National Archeological Museum, 30 to the Arch of Hadrian/ Temple of Zeus/ Athens Agora/ Acropolis / Parthenon). Christos was very helpful with explainign transport from the airport and with every other question I had.