Efi and Anna's is in a great location, close to the the metro that gets you to the airport in around 45 minutes and a walkable distance from most attractions around Athens. You'll also be right in the centre of Athens' hip/bustling neighbourhood of Psirri, filled with cool restaurants, bars and coffee shops.
The apartment itself is cute and offers an amazing view of the Acropolis right from your bed and personal terrace. I'd definitely stay here again!