I haven't been to all of them so it would be impossible to say, although I thought Santorini was very beautiful in a very stark way.
Still, I prefer more green, nature a bit tamed, so my favorite (of the ones I've seen) is Capri, which isn't even listed.
The Gardens of Augustus:
You can climb down this incredibly long staircase hewn into the rock to reach Da Luigi at the foot of I Faraglioni. The trip back up is a "trip" if you know what I mean, but you can wimp out and go by boat.
It was one of my best vacation days ever. Food is great too.
These pictures don't even begin to do it justice.
Da Luigi: more glorious pictures on their website, along with pictures of the great food:
https://www.luigiaifaraglioni.com/
A famous commercial is set on Capri near these rocks: the Dolce and Gabbana light blue commercials. They're risque so I won't link to them, but they do capture the scenery very well.