Kos or Santorini?

Kos is the better beach island by a distance. It has long, open sand from Tigaki through Marmari to Mastichari, with shallow water and room to spread out. The calmer, clearer coves are in the south around Kardamena and on the Kefalos peninsula, where Paradise Beach and Agios Stefanos are the prettiest bays.

Santorini's beaches are volcanic black sand and fine pebble that burns underfoot by midday. Perissa, Perivolos and Kamari are comfortable, and Red Beach is striking but small. Anyone staying in the caldera villages has to travel down to the coast to swim. On both islands the meltemi can roughen the exposed shores in high summer.

Santorini eats and drinks better, mostly because of what its volcanic soil grows. There is fava from yellow split peas, tomato fritters, white aubergines and capers, and above all the wine. Assyrtiko and the sweet Vinsanto can be tasted at wineries around Pyrgos, Megalochori and Exo Gonia, though many cliff-edge tables mostly charge for the sunset.

Kos offers friendly, straightforward island cooking, with grilled octopus, chickpea pitaroudia and krasotyri cheese aged in red wine. It is best in Zia, Pyli and the harbour tavernas at Mastichari. In the big resorts, much of the food is aimed at all-inclusive guests.

Santorini has the stronger heritage, and its two strengths are of different kinds. Akrotiri is a Bronze Age town preserved under volcanic ash, with frescoes on show in Fira. The second strength is the islands' built landscape: cave houses and blue domes on the caldera rim, and the medieval kastelli of Pyrgos and Emporio.

Kos is about Roman and Hellenistic ruins scattered through a working town: the Agora, the Odeon, the Casa Romana mosaics and the Knights' Neratzia Castle by the harbour. Its finest site, the Asklepieion, is a terraced healing sanctuary just outside town. Either island's sights fill two or three days.

Kos is the island for a proper night out. The lanes of Kos Town's old quarter are full of bars that stay loud into the small hours, and Kardamena is an out-and-out party resort with late clubs and a young Northern European crowd.

On Santorini, evenings are built around sunset, dinner and a cocktail facing the caldera, which suits couples more than night owls. Only a few lanes in Fira keep clubs going late in high summer. On both islands, going out stops almost entirely in winter.

Santorini's scenery is the reason many people go. Ash-and-lava cliffs drop more than 300m into a flooded volcano, and the 10km rim path from Fira to Oia is one of the great walks in the Aegean. Boats cross to the black cone of Nea Kameni, and divers explore the submerged caldera walls.

Kos is gentler and greener in places. Pine woods climb the Dikeos range to Mount Christos for the sunset, peacocks wander in the Plaka forest and flamingos winter on the Alikes salt lake. Where it does better is wind and wheels: Marmari and Tigaki are good for windsurfing and kitesurfing, and the flat coast is easy to cycle.

Both islands' day trips go by sea, and Kos has the slight edge thanks to its range and easier logistics. Bodrum is a short ferry ride away, so you can add a Turkish castle and bazaar if you bring a passport. Nisyros offers a walk into a volcanic crater, and Kalymnos is a quick crossing from Mastichari, with boats leaving from three ports.

From Santorini, Thirasia is a quiet caldera crossing, and Ios, Folegandros and Naxos are within reach. A long day can even take in Knossos on Crete. However, almost everything leaves from the single port at Athinios, and timetables thin sharply outside summer.

Kos is clearly the family island. The beaches at Tigaki, Marmari and Mastichari shelve gently into shallow water, many resorts come with pools and kids' clubs, and there is a large water park near Marmari. Families can also cycle together on the flat paths around town.

Santorini's caldera villages are hard going with children: steep steps, crowds, no pushchair access and cliff hotels that often refuse young guests. Kamari and Perissa work far better, with flat promenades and a small water park, and older children enjoy the volcano boat. Neither island has a zoo or aquarium.

Getting around Kos is simpler. The island is long and flat along its coast, buses link Kos Town, the airport and the main resorts, and cycle lanes run to the beaches either side of town. You only need a hire car for the hill villages and the far south-west.

On Santorini, distances are short but progress is slow. Every bus route runs through Fira, so cross-island trips mean changing there, and the buses are packed in summer. Narrow roads and scarce parking in Oia add to the delays, and the caldera villages are steps on foot. Fira is the only practical base without a car.

Santorini offers more to browse, although neither island is a shopping destination. The cliff-top lanes of Oia and Fira have galleries of island painters and photographers, jewellers near Fira's cathedral, and linen and ceramics. The best things to take home are bottles of Assyrtiko and Vinsanto, capers and fava.

Kos Town's old quarter is mostly souvenirs, leather and sandals. Its Italian-era market hall on Eleftherias Square is good for herbs, spices, honey and olive oil, and the resorts offer little more than beach shops.

Kos is much the cheaper of the two. Because it is built for package travel, it has plenty of mid-range apartments in Kardamena, Tigaki and Marmari, and tavernas, buses and archaeological sites cost little. Harbour-front meals and sunbeds are where costs add up.

Santorini's prices are driven by the view. Cave suites on the rim at Oia, Imerovigli and Fira are among the dearest rooms in Greece, and boat trips and tastings add more. Keeping costs down there means staying in Kamari or Perissa and walking up to watch the sunset. Both islands are cheaper outside July and August.

Neither island is worth choosing for performances, and both go quiet outside summer. The difference is in the settings. Kos stages its Hippokrateia festival in the Asklepieion, the Roman Odeon and the castle, and village saints' days bring Greek music and dancing. Santorini's main event is a classical music festival in Fira at the end of summer, with occasional concerts in old mansions and wineries.

The two are about even for a restful stay, but they offer opposite kinds of rest. On Kos, the highlight is Therma, a free hot sulphur spring running onto a pebble beach, where bathers pile stones into pools. The rest of the time, unwinding means slow days around Kefalos or in Zia and Pyli.

On Santorini, rest comes from the luxury cave hotel at Imerovigli or Oia, with a heated plunge pool facing the caldera, plus a boat swim into Palea Kameni's warm, rust-coloured spring. For quiet, choose Imerovigli or the inland wine villages, not the crowded rim at Oia and Fira.