Just came back from 2 weeks in Greece, summer is still around the corner but most places are already very crowded with tourists. I'd go back in the 'shoulder seasons' of early Spring or Fall, as advised by many locals. Temperatures and prices lower.
I went to the exclusive and expensive Hotel Grand Bretagne, on Syntagma Square, and found its all-out luxury decoration too much, too old. Then there are the frequent demonstrations on the square, and they can be noisy.
Our hotel, quite comfortable but much less fussy or pricey, Hermes Hotel, was few blocks away from GB, on a quiet street close to shopping and convenient to the pretty Plaka area, where we dined every night. Also, the girls at the front desk were very helpful and friendly.
I'll definitely stay there next time in Athens.