3rd port option; Lavrio by thanalik
Lavrio is the future main port of Athens,though is still not so well orginized. Is in the SE edge of Athens coast,a few km. away from cape Sounio and with easy access from airport through Athens ring-road,AttikiOdos. Is good to organize a tour to Sounio and then ship from Lavrio. I still dont have infos to upload about schedules or sites, but for sure i'll have update this page till summer period.
Maybe you also ask your travel agent, of google for it.