We had a great time in Athens staying in Marina's apartment. She was very nice and accommodating, the location was very central. However, there were a few problems we encountered. There was only one bathroom and one toilet, and the ceiling of the whole second floor (including the bedrooms) was connected, which means there was very little privacy. However, if you are not traveling with your colleagues then these things shouldn't be a problem.
I would certainly recommend Maria's apartment.