We just got back from our Greek Island cruise and when we were in Athens, we took my cousin's recommendation for a private tour.
It was a great day. It was much better than being packed in a bus and taken out on the agenda of the tour provider. This way, our driver, Fotis (Foti), took us to where we wanted and recommended the best route to see everything in the time allotted.
The price was reasonable...about the same price for the 7.5 hours we were with him as we would have paid for only 4 hrs on the ship's excursion.
We saw everything we wanted at the pace we wanted.