Dioni's place is the perfect spot for a small family or couple. It has great views, especially for the morning sunrise, and is very private. You do have to walk up to the top of the town, but as long as you're relatively fit, it shouldn't be an issue. It took us about 5-10 minutes. It's a great place to have as a home base to explore Sifnos. Make sure to check out the walking trails, number 5 was our favorite.
The wifi can be nonexistent or spotty, so make sure to do your research/check your emails in town at a cafe before you head back up the hill.