I have stayed at the Airotel Stratos Vassilikos Hotel and the Airotel Parthenon. Both were great. The Stratos Vassilikos is well away from the demonstrations at Syntagma and is quite lovely. Breakfast buffet is exquisite. Parthenon is not as fancy, but also has a great breakfast buffet and is steps from the Dionysiou Areopagitou, which is the long boulevard from which you can easily access the Acropolis, Plaka, Lofos Filopappou, the new museum, etc.