Milos is volcanic — white moonscape cliffs, hot springs, surreal rock formations like Sarakiniko. Sifnos is greener and more agricultural, with terraced hillsides, dovecotes, and 365 chapels.

Milos wins for dramatic photography. Sifnos wins for slow walking.

Milos has more variety — over 70 beaches, many only reachable by boat, in colours from white to red to black. Sifnos has fewer but more swimmable, family-friendly bays on the south coast.

Milos wins for beach-hopping. Sifnos wins for one-beach-all-week.

No contest — Sifnos is the culinary capital of the Cyclades. Milos eats well, but Sifnos has pottery dishes, slow stews, and a chef tradition going back a century.

Milos has grown fast in the last decade — more crowds, more Instagram, more rental cars on narrow roads in August. Sifnos is still mostly Greek-and-French-and-Italian, quieter, with later dinners and earlier mornings.

Milos has an airport with daily Athens flights. Sifnos is ferry-only (2h 45 from Piraeus on the fast boat, 5h on the conventional). If you have one week and you're flying in, Milos is logistically easier. If you have ten days or a ferry-tolerant schedule, Sifnos is more rewarding.