Where's the best place to experience Orthodox Easter in Greece?

I don't know what's biggest and best, but where Rick chose to film the Greek segment of his European Easter show was in Nafplio, already one of his favorite towns for a nice combo of medium size, real-life, and proximity to the ruins at Mycenae and Epidavros.

Years ago, I happened to be in Chania, Crete at Easter and enjoyed their Good Friday candle-light procession around town. A restaurant gave patrons each an Easter bread to take home and an old lady insisted that I take a seat in the church instead of standing at the back. I expect that most towns have something going on. But how to get invited to a roast lamb feast is a harder question.

Consider the village of Pyrgos on Santorini:

https://www.youtube.com/watch?v=xfs3oh_Z5lY

https://www.youtube.com/watch?v=0F1EtGN0Lio

Or Chios: https://www.youtube.com/watch?v=v0j62StjKW4

We will be in Greece at that time and have some flexibility.

Well, wherever you decide to be, make reservations early. I am sure all the nice places will be overcrowded with Greeks visiting their families for the holidays.

But how to get invited to a roast lamb feast is a harder question.

That would probably depend on if they celebrate it purely as a family festivity (like many people here do Christmas), or if it includes hospitality to strangers.

I haven't had the opportunity to experience orthodox easter unfortunately (would love to!), but I have experienced some saints' days with church festivities. Those are open to everyone, and you get invited in faster than you can say "Christos anesti".