With kids, it depends on the day.
Hydra is the connoisseur's island day: no cars, no scooters — just donkeys, sea-captains' mansions, swimming off the rocks and a harbour that's pure cinema. The catch: there are no sandy beaches (it's rocky swims off ledges), it's pricey and artsy, and a day-tripper only gets a few midday hours before the return ferry.