This place was it. Me and my friend stayed in Athens for five months, and couldn't have asked for a better flat. It is large, it has all necessary amenities and is located in a quiet area, still close to the absolute central parts of Athens (me and my friend both walked to our daily occupations). There is a gym and several stores nearby, and many bus-lines on the huge avenue where also the metro station is located (the avenue can be busy and noisy, but you don't really notice it since the flat is on a dead parallell street and has the bedrooms facing away from the road. The flat is surrounded by bars and restaurants and we ate in the area almost every evening.
The flat itself is spacious and very bright, with large windows in every room (which can be opened to the balconies). The balcony of the living room is really cozy and we hung out there all the time when the weather allowed (which is long time in Greece compared to native Sweden). There are many bedsheets and towels so the place is suitable also for a longer stay and allows for lighter packing during flights (or saving money from buying these things from outside).
Would definitely recommend to anyone! We had friends over who thought our place was the best compared to others they had been to in the city.