Sifnos is a gem, green, rocky, and filled with nice people, among the beautiful Cyclads. And Ano Petali is pretty much perfect for its position which is and unexpected great balance of convenience (two of the biggest villages are literally 5/10 minutes away) and quiet. So imagine how hard it would be to make things even better.
Yannis (Katerina's husband) welcomed us heartily in an unbelievable corner of paradise, with a great orchard that gave us more than one exquisite meal, and a small but cozy apartment that had everything you could ask. As somebody else already said in another review, just go there, and stay. You won't ever want to leave.