Concierge.com's insider take:
One of the prettiest of the Cyclades, Sifnos is friendly, accessible, varied, and green in the center, with great beaches and great food (Greeks believe Sifniot chefs are the best). Also, there are 365 churches. The port, Kamares, could easily suffice for an entire vacation. It has an OK beach, but buses and boats make everywhere else accessible. Apollonia is the capital, high up and inland, throbbing (though more gently than the notorious party islands) at night, peaceful and pretty by day. The ancient village of Kastro on the east coast, dating back to 3000 B.C., is so unspoiled you can imagine the centuries rolling back. Platys Yialos is the big, big beach, which sucks up most of the mass tourism, and tiny Vathy, a beach with a fishing village attached, is heavenly and not (yet) ruined by its newly paved access road.