Temple of Poseidon at Sounion

You mentioned almost all the ways to go to Cape Sounion. But the best way for you, no one can guess.
This is the one you prefer based on your own personal criteria.

:

By public bus it's about 2 hours drive and €15 one way.

By taxi it's about 1h15 drive and €75 one way

Or with a private driver it's around €200 for half a day

Example here:

https://traveler.welcomepickups.com/en/athens/sightseeing_rides/cape-sounion

With a tourist bus it is around €40

Or you can rent a car for the day.

It's not a popular option at this newsboard, but we took two full-day tourist bus excursions from Athens, because I didn't want to drive a car in Greece. One of them had a full stop and walkaround at Sounion, although it was a minor part of the trip. We found the excursions very worthwhile. I can't remember the exact division of sights, but a big sights those two days included Delphi, Napflio, Corinth Canal, Epidaurus or was it another major theater. I was really pleased when the guide responded cheerfully to our request to be LEFT at Delphi, while everyone else went to a restaurant lunch. We had hot dogs from a booth, and enjoyed over an extra hour at Delphi. We made it our business to be waiting at the side of the road at the promised time, of course.

We did a tour with Getaways Greece and had a great time. They picked us up at our hotel in the afternoon. We stopped at a beach where we were able to buy drinks and dinner (which was delicious!). We had time to swim but we went in late October and the water was too cold. It was actually nice to just sit and enjoy the sun and the view. We then went to the Temple of Poseidon at sunset. Our guide made it interesting and fun and we had a great time.

Thanks to all for these tips.