Kos or Mykonos?

Both islands are built around sandy beaches and both are very good, so the choice is about style. Kos gives you space: long, open strands from Tigaki to Mastichari with shallow water, though the meltemi can make the north coast choppy, and its prettiest bays lie far out on the Kefalos peninsula at Paradise Beach and Agios Stefanos.

Mykonos packs a run of distinct south-coast bays into a short stretch, from sheltered Ornos to the party beaches of Paradise and Super Paradise, with notably clear water. Many are lined with organised sunbeds and beach clubs, so it feels more groomed and social than Kos, and true quiet means heading to the eastern coves or the windy north.

Mykonos has the more interesting table, though neither island is a food destination. Its own specialities, the peppery kopanisti cheese, cured louza and almond sweets from Chora's bakeries, sit alongside a large high-end scene of sushi and fusion that is polished if sometimes more about being seen.

Kos eats more simply: grilled fish and meze, pitaroudia and wine-matured krasotyri, best found in Zia, Pyli or the harbour at Mastichari. In the big resorts much of the cooking is pitched at package and all-inclusive guests, which is where Kos falls behind.

Delos is the decisive difference. A short boat ride from Chora brings you to one of the great religious sanctuaries of ancient Greece, and Chora itself, with its windmills, Little Venice and the Paraportiani church, is a sight in its own right.

Kos has more history on the island itself, with Roman ruins scattered through Kos Town, the Knights' castle on the harbour and the terraced Asklepieion above it. It is rewarding for two or three days, but nothing on it matches the scale of Delos.

Mykonos is the far stronger choice for going out. Its nights run from afternoon beach clubs through Little Venice sunsets and Chora's cocktail and dance bars, shaped by a long-established gay scene, to big clubs with international DJs that close at sunrise.

Kos has two hubs rather than an island-wide scene: the loud bar lanes of Kos Town's old quarter and Kardamena's young party resort. Elsewhere evenings end with a seafront drink, which many families and couples prefer.

Kos has more landscape to explore. The Dikeos range rises to over 800m behind Zia, with pine-wood trails up to Mount Christos, and there are peacocks in the Plaka forest and flamingos on the Alikes salt lake in the cooler months.

Mykonos is low, bare and rocky, lovely for its light rather than its walking. Its outdoor appeal is on and under the water: the same summer wind drives kitesurfing at Korfos and Kalafatis as it does at Marmari on Kos, but Mykonos adds diving around reefs and wrecks.

The two are broadly level, and every outing from either goes by boat. From Kos the trips change country and scenery: Bodrum's castle and bazaar across the water in Turkey, the volcanic crater on Nisyros and the sponge-diving harbour of Kalymnos.

From Mykonos you hop around the Cyclades instead, to pilgrim Tinos, neoclassical Ermoupoli on Syros, or Paros and Naxos on fast boats. There are more islands in reach, but they are more alike, and the meltemi can disrupt crossings.

Kos is far better suited to children. Gentle north-coast shallows, resorts with pools and kids' clubs, a water park near Marmari, short flat distances and tavernas happy with children up late make daily life simple, though there are no zoos or museums aimed at them.

Mykonos can work with care, at calm bays such as Ornos or Platis Gialos, and Delos may grip older children. But the island's identity is adult nightlife, Chora gets loud late in summer, and the windy north coast is risky for small swimmers.

On Kos, buses and bicycles do most of the work. Buses run along the main road from Kos Town to the big resorts, cycle lanes lead from the flat, walkable town to the beaches on either side, and you need a hire car only for the hill villages and the far south-west. It is the simpler island to manage without a car.

Mykonos is smaller, and here you get about on foot and by boat. Chora is entirely car-free, and sea taxis are a pleasant way between the south-coast beaches. Against that, taxis are scarce in summer, the roads around Chora are narrow and congested, and you need your own wheels for the quieter north and east.

Mykonos is the better place to shop, within limits. Matoyianni Street and the alleys around it hold designer resort wear, fine Greek jewellery, galleries and small design shops open late into the evening, though most of it is beachwear and much closes out of season.

Kos offers mainly souvenirs, leather and sponges in the old-quarter lanes. Its best buys are edible: olive oil, honey and the herbs and spices in the Italian-era market hall on Eleftherias Square.

Kos is much the cheaper island. Built for package travel, it has plenty of mid-range rooms in Tigaki, Marmari and Kardamena, inexpensive buses, bike hire and back-street tavernas, and its ancient sites cost little, leaving overall costs near mainland Southern Europe.

Mykonos in season is priced for a luxury crowd, from hotel rooms and beach-club sunbeds to taxis and car hire. Staying inland or at Ano Mera, eating gyros and travelling by bus all help, but it never becomes a budget trip in summer.

Neither island has any real theatre or concert life, and both are quiet out of season. What Kos does have is the summer Hippokrateia festival, staging concerts, theatre and dance in the Asklepieion, the Roman Odeon and the castle, along with Greek-night shows in the resorts. On Mykonos the music is mostly club and beach-bar DJ sets, with only the occasional open-air concert or village festival.

Therma, on the south-east coast of Kos, has no equal on Mykonos. A hot sulphur spring runs down to the sea, and bathers pile up pebbles to make pools where the hot water mixes with the waves. The hill villages of Zia and Pyli and the quiet coast around Kefalos keep the rest of a stay slow.

Mykonos has no bathing tradition of its own, so wellness there means upmarket hotel spas and yoga terraces. Its summer rhythm works against rest. Calm comes mainly at Agios Sostis, at Ftelia or beyond Kalafatis, or in early June and late September.