Kos or Zakynthos?

Both islands are built around their beaches, and for sand and warm water they are close. The difference is in the setting. Kos has long, open strands on the north coast from Tigaki to Mastichari, where the summer meltemi can make the sea choppy. For calmer water there are sheltered coves around Kardamena and the lovely Kefalos bays in the south-west.

Zakynthos packs more variety into a smaller space. It has the sweep of Laganas Bay with its protected turtle beaches, the sandy coves of Vasilikos, rocky west-coast inlets like Porto Limnionas and boat trips to swim at the Blue Caves. Its pale-blue water over white limestone is the more striking, though resort sunbeds fill up in high summer.

Neither island is a food destination, and both serve honest taverna cooking with a few local specialities worth seeking out. Zakynthos has slightly more of its own: garlicky skordostoumbi, ladotyri cheese kept in oil, mantolato nougat and Verdea wine poured in the villages around Keri.

Kos has pitaroudia chickpea fritters, krasotyri cheese matured in red wine and a few small wineries near Kefalos. Its best meals are in Zia and Pyli and by the harbours at Mastichari and Kamari, while the resort menus are aimed squarely at package tourists.

Kos has far more to see. In Kos Town the ancient past lies open among the streets: the Agora, the restored Odeon, Roman mosaics and the Casa Romana, with the Knights' Neratzia Castle at the harbour. The terraced Asklepieion sits on the hillside above. Add Old Pyli and Antimachia castle and you have two or three full days.

Zakynthos lost most of its Venetian capital in the 1953 earthquake. What remains is a half-day circuit: the Ionian icons in the Byzantine Museum, the Solomos museum, the castle on Bochali hill and the monastery of Anafonitria.

Both islands do their summer partying in one or two places, but the shape differs. On Zakynthos it is Laganas, a single long strip of clubs, foam parties and drinking until dawn, aimed at young British groups and the bigger party of the two. Kos divides its nights between the bar-packed lanes of Kos Town's old quarter, which draw a more mixed crowd, and the club resort of Kardamena.

Away from those places, evenings on both islands end with a quiet drink, and both scenes close almost completely after September.

Zakynthos is the island for scenery. High white limestone cliffs line its west and north, with great viewpoints at Keri and above Navagio and sea caves around Cape Skinari. Laganas Bay is a marine park where loggerhead turtles nest, and the diving, snorkelling and kayaking along the coast are good.

Kos is flatter and drier, and its outdoor appeal is quieter. There are pine-wood walks up the Dikeos range to Mount Christos, flamingos on the Alikes salt lake and peacocks in the Plaka forest. The steady wind at Marmari and Tigaki suits windsurfers and kitesurfers.

Kos is much better placed for days off the island. Bodrum on the Turkish coast is a short ferry ride away, and Nisyros, with its volcanic crater, is about an hour by boat. Kalymnos, Pserimos and Plati are close enough for an easy outing too.

From Zakynthos the choice is narrower. There is a summer ferry to southern Kefalonia, or the mainland crossing to Kyllini for Chlemoutsi castle and, on a long day, ancient Olympia. Most visitors settle for a tour of their own island.

Both work well with young children. Each has gently shelving sand, resort pools and kids' clubs, a large water park and tavernas that welcome children. Kos is a little easier from day to day: the land is flat, families cycle together on the paths around Kos Town, and older children get castles and ruins as well.

On Zakynthos, families do best on the north-east coast around Tsilivi and Alykes, and boat trips to spot turtles are a highlight. Several of the famous beaches, though, mean a steep path or a boat ride.

Kos is simpler to get around. Kos Town is flat and easy to walk, cycle lanes lead to beaches either side of it, and buses run along the main road to the resorts. You only need a car for a day or two in the south-west and the hill villages.

On Zakynthos the buses reach the main resorts but not the cliffs, viewpoints and villages of the west and north, where roads are narrow and winding. To see much of the island, plan on a car, a scooter or organised boat trips.

Kos Town's old quarter gives you more to browse. Among the leather, sandals, sponges and beachwear there are a few better shops for olive oil, honey and ceramics. The Italian-era market hall on Eleftherias Square sells herbs, spices and local produce.

Zakynthos Town has Alexandrou Roma, a practical street of local shops and some clothing, and the resort strips offer little beyond beachwear. The souvenirs most worth taking home are thyme honey, olive oil and other things to eat, plus lace and weaving from the villages around Volimes. If you want fashion or design, you will find almost nothing on either island.

Costs are much the same on both islands, since each is built around package travel, with plenty of mid-range rooms and reasonable tavernas. The extras differ. On Kos, cheap buses and bike hire keep getting about inexpensive. On Zakynthos, boat trips and car hire add up over a week, because so many of its best sights can only be reached that way.

Neither island has a theatre or concert season, and on both the resort entertainment runs mostly to Greek dancing nights. The difference is in character. Kos has the summer Hippokrateia festival, with concerts, theatre and dance staged at the Asklepieion, the Roman Odeon and the castle.

Zakynthos has a living folk tradition instead. Kantades and arekia serenades are sung informally in tavernas, the town's old philharmonic band plays at religious feasts, and villagers perform omilies street theatre at carnival.

Kos offers more for unwinding, above all at Therma. There a hot sulphur spring runs onto a pebble beach, and bathers stack stones into pools where it mixes with the sea. Quiet days around Kefalos, Mastichari and the hill villages of Zia and Pyli do the rest.

Zakynthos relies on its slow pace and hotel spas. Its sulphur springs at Xigia are cool rather than hot, and finding real calm means staying around Keri, Agios Leon or Vasilikos, well away from Laganas.