Voyager, Apollo, and Hubble. Everything else NASA has done is a distant 4th place. And it's not like 4th place is trash, it's just that the big 3 are just so impressive.
I don't think Apollo was very interesting or useful beyond cold war propaganda. Yes, we're capable of amazing things—but putting a man on the moon pales in comparison to basic healthcare funding. Why must we insist on wasting billions on histrionic braggadocio when we can't perform the basics of a modern society?
James Webb Telescope is up there with Hubble.