I have been to Greece, but it was many years ago on my after college backpack through Europe tour. I don't think you'd want to stay where I stayed - mostly youth hostels!
I wasn't that impressed with Athens, but I wasn't an age where much impressed me. I did like the Acropolis, but it was a very hot day.
I did adore Santorini - loved it there. It was just an incredibly beautiful island with very friendly people. I always think back to it being the most beautiful place that I've ever gone.