I have visited Olympia and found it interesting and enjoyable. As a first time visitor to Greece, that would be my choice. It is one of the top attractions in Greece.
I looked up Pylos, and it also looks an interesting day tour - scenic too.
So, the choice depends on your interests
Comments
It depends on why you are going to Greece. If you are into ancient history and ruins - Olympia.
I have visited Olympia and found it interesting and enjoyable. As a first time visitor to Greece, that would be my choice. It is one of the top attractions in Greece.
I looked up Pylos, and it also looks an interesting day tour - scenic too.
So, the choice depends on your interests