Mykonos or Rhodes?

Both are true beach islands, and the difference lies in the sand and the scene. Mykonos's south coast offers sandy bays with very clear water, and each has a distinct mood: sheltered Ornos close to town, polished Psarou, party Paradise, and roomier Elia and Kalafatis. Beach clubs and rows of sunbeds set the tone on many of them.

Rhodes has a longer chain of sheltered east-coast bays from Faliraki to Lindos, often with sand mixed with fine shingle. The highlights are Tsambika's soft sweep, the snorkelling inlets of Anthony Quinn Bay and St Paul's below the acropolis. Its sea is a little warmer and its swimming season a little longer, and Prasonisi adds a sandbar between calm water and waves.

The two islands are about level for food, but they reward different approaches. On Mykonos the meal is mostly about the setting: grilled octopus by the water in Little Venice, island specialities such as kopanisti and louza, and a large, showy tier of sushi and celebrity-chef dining.

Rhodes has less glamour and more substance away from the resort buffets. Pitaroudia, matsi pasta and slow-cooked goat come from the family tavernas in the inland villages, alongside souma and wine from Embonas. Getting the best out of it means driving inland rather than dressing up.

Rhodes has far more history to explore. Its medieval Old Town, one of Europe's most complete fortified towns, runs from the Street of the Knights to the Palace of the Grand Master, with mosques, a synagogue and the dry moat along the way. Beyond the walls are the acropolis of Lindos, ancient Kamiros and Monte Smith, and together they fill several days.

Mykonos has one outstanding sight in Delos, the sacred island of Apollo, which deserves a full morning. On the island itself, Chora's whitewashed maze, the windmills at Kato Mili and Paraportiani church make a lovely but short programme, done in two or three days.

This is where Mykonos pulls well ahead. The night begins at the Paradise and Super Paradise beach clubs in the afternoon, moves to Little Venice for sunset and then to Chora's dance bars, shaped by a long-established gay scene, before the big clubs carry on until sunrise.

Rhodes has pockets rather than a whole island given over to the night: Faliraki's strip for young package crowds, one late lane in the Old Town, and stylish rooftop bars in Lindos. In most of its coastal resorts the evening ends at the hotel bar.

Rhodes is the greener and more varied island. Pine-covered hills, the shaded gorge of the Valley of the Butterflies and the wooded stream at Seven Springs make good walking in spring and autumn, and Mount Attavyros offers a real climb above the wine villages.

Mykonos is low, bare and brown, beautiful for its light and sea more than its land, and walkers are limited to lanes and coastal paths. Both islands use their wind well: Mykonos has kitesurfing at Korfos and Kalafatis plus good diving, while Rhodes has Prasonisi, one of the Mediterranean's best-known windsurfing spots.

The day trips are about equal, and on both islands they depend on boats and summer seas. From Mykonos the ferries reach other Cycladic islands, such as pilgrim Tinos, neoclassical Ermoupoli on Syros, and Paros and Naxos, so the variety is between similar islands.

Rhodes has a smaller set but a wider spread. It offers the pastel harbour of Symi, quiet Halki, and a crossing to Marmaris for a taste of Turkey. It also has more to do by car on the island itself, with the castles of Monolithos and Kritinia and the potters of Archangelos.

Rhodes is much the easier island with children. Tsambika, Afandou and Kolymbia have gently sloping sand, the big east-coast resorts run pools and kids' clubs, and there is a water park above Faliraki and an aquarium in Rhodes Town. The main thing to plan around is the July and August heat.

Mykonos can work if a family picks a calm bay such as Ornos or Agios Stefanos, hires a car and comes in June or September. Beyond the water park near Elia and a trip to Delos, though, little is aimed at children, and Chora gets loud late into the night.

Neither island is effortless, and they are awkward in different ways. Mykonos is small, with nowhere much more than half an hour from Chora. Buses and handy sea taxis cover the south-coast beaches, but there are too few taxis in summer, the roads are narrow and congested, and the north and east need a car or scooter.

Rhodes is bigger, and the distances show: it takes about an hour and a half to drive to Prasonisi. On the other hand, its main roads are good and the east-coast buses to Lindos are reliable. Rhodes Town and its car-free Old Town are easy on foot.

Mykonos is the better place to shop for style. Matoyianni Street and the lanes around it are full of designer resort wear, linen, swimwear and fine Greek jewellery, and the shops stay open late for evening browsing, though almost everything is fashion and almost nothing is local craft.

Rhodes is mainly souvenirs along Sokratous Street. Still, it has things Mykonos lacks: Lindian-style painted ceramics from Archangelos, village lace and embroidery, and honey and wine from Embonas.

Rhodes costs far less. Its many package hotels and all-inclusive resorts keep the north and east coasts moderately priced, and village tavernas and buses are reasonable. Only Lindos and the boutique hotels of the Old Town reach high prices.

On Mykonos in summer, rooms, cocktails, sunbeds, taxis and car hire are all priced for a luxury crowd. Staying around Ano Mera, eating at bakeries and visiting in June or late September all help, but the island never becomes cheap.

Neither island is somewhere to plan a trip around performances, but Rhodes has a little more. A long-established company performs Greek folk dance in a small Old Town theatre in season, and there are summer concerts in the medieval moat and the ancient stadium. On Mykonos the music is mostly the DJ sets of its clubs, with only the odd village festival or open-air concert.

Rest comes a little more easily on Rhodes. The quiet south, with villages such as Lahania and Asklipio, offers long meals, backgammon in the kafeneio and dark, clear skies far from the resort strip, and the big east-coast hotels have good spas.

On Mykonos, wellness means hotel spas with yoga facing the sea. Real calm means retreating to Agios Sostis, Ftelia or the bays beyond Kalafatis, or coming in early June or late September, when the party rhythm eases.