Kalliopi's apartment was the perfect choice for me.
A couple of reasons to stay there: Close to the center; I could walk everywhere. Amazing kitchen for shared use, gorgeous terrace and great host - reliable and kind.
Mets is a great area because it is a bit calmer, less touristic and has nice local bars and parks.
Keep in mind that the guest room connects to the living area with only a steep staircase, thus, if you are limited in movement, this may be difficult; same if you want lots of privacy as a couple. There was moderate noise from the neighbours at night, nothing that bothered me really, though it might present as an issue to light sleepers.
For young folks like me, just an awesome stay!