If you are looking for an affordable, center located and clean accomodation, I would totally recommend Sleep Easy!
Though, don't be surprised when you arrive for the first time and you don't see the entrance of the building, it's hiding there somewhere ;) If you are not sure the locals are helpful to give you some guidelines!
The hosts are super nice, helpful and patient! When I arrived I had some issues and delays at the airport, and they were incredibly patient with me. The cleaning stuff do a very useful job and they kept everything clean and safe, which I am incredibly grateful for.
In total, Sleep Easy was rather a Sleep cosy space for my staying in Athens, I felt safe in the neighbourhood and everything was in reachable distance.