In my opinion, Nikolas' flat is definitely the place to stay in Santorini. It has a lot of charm, an amazing view on the sea, and there is a little beach down the stairs. It is fairly remote, so you will be pretty much on your own, which has no price on a somewhat touristic island. You will therefore need to rent a car, but preferably a quad or a scooter, to be able to enjoy the rest of the island. Nikolas is as sweet and caring as they come. I would definitely go back there if I were to return to Santorini.