We loved Folegandros. Small, but wonderfull. Perfect for 3-4 days. The appartment is practically on the beach. In spring, the area in Agkali is very nice. Quiet calm in fact. But it's supposed to be full of people in summertime...
I recommand that appartment, but It needs more equipement in the little kitchen.
The owners, Margarita and Dionisis, are kind and welcoming. They helped me to rent a car.
By the way, they have a very good restaurant in the old town : Belegra. Good food and good atmosphere.