Recommendation for Santorini

I'm going to Santorini for a week in early September with my (new) girlfriend.

Can anyone recommend a good part of the island (and maybe specific hotel) to stay? We are early/mid 30s, want somewhere low-medium density - not too crowded but not completely secluded, perhaps a village somewhere on the island, preferably with a good beach and some good restaurants and a couple of interesting things to do?!?

Alternatively, any recommendations for a nearby island that fits the same criteria? I've heard that Sifnos, Folegandros, Amorgos are all good - I'd appreciate any comments.

Thanks.