Kefalonia or Peloponnese?

Both have outstanding coasts in clear, warm water, and the swimming season is the same. Kefalonia's beaches are more dramatic and closer together: the white pebble crescent of Myrtos under its cliffs, Petani and Antisamos below green hills, with sandier stretches at Skala, Lourdas and Xi.

The Peloponnese spreads its beaches along a much longer coastline and has more sand. There is the horseshoe of Voidokilia and Navarino Bay in Messinia, the pale turquoise shallows of Elafonisos and the pebble coves below Mani villages. On Kefalonia the beach is the main event. On the mainland it is one part of a broader trip.

The Peloponnese eats better and with more variety. It has Kalamata olives and oil, slow-cooked goat, the Mani's cured pork and fish grilled at harbour tables. It also has serious wine country: red Agiorgitiko from Nemea and Moschofilero from the Tripoli plateau. Kalamata and Nafplio give real choice, and Kalamata's covered market is worth a morning.

Kefalonia has dishes of its own, such as the spiced meat pie, aliada with salt cod and the red almond mandoles. It also makes crisp Robola in the Omala valley. Beyond Argostoli, though, menus repeat from one taverna to the next.

This is the widest gap between the two. The Peloponnese holds Olympia, Mycenae, Tiryns, Epidaurus, Messene and Bassae. On top of that comes a medieval layer: Mystras, Monemvasia and the Venetian castles of Methoni and Koroni. Nafplio makes an elegant base for much of it.

Kefalonia lost most of its old buildings in the 1953 earthquake. Fiskardo's Venetian houses, the fortress at Assos, the Castle of Agios Georgios and the tholos tomb at Tzanata are good outings. They fill a few mornings, not a whole trip.

Neither is a party destination, and in both an evening mostly means dinner and a drink by the water. The Peloponnese has more going on. Nafplio's old town and Kalamata's seafront stay busy late, and Patras, a university city, has whole streets of bars and clubs.

On Kefalonia, late evenings centre on Argostoli's main square and the Lithostroto, with a strip of cocktail bars at Lassi. Outside July and August, most places are quiet well before midnight.

Kefalonia packs its outdoors into one island. There is the dark Greek fir forest of Mount Ainos, with semi-wild horses and summit views across to Ithaca, and the tall white cliffs of the west coast above Myrtos and Assos. Below ground are the karst caves of Melissani, where boats cross a blue lake lit through a gap in the roof, and Drogarati with its stalactites. Sea kayaking off the north-east coast and turtles in Argostoli harbour complete it.

The Peloponnese has far more ground and more variety. Taygetos climbs to about 2,400m above the Mani villages, the Lousios gorge links cliff monasteries with Dimitsana and Stemnitsa, and the long, well-marked Menalon Trail crosses Arcadia. Add the Vouraikos gorge with its rack railway, winter skiing on Chelmos and migrating birds at the Gialova lagoon, and a walker has enough for a much longer trip.

The Peloponnese offers far more outings. From Nafplio, Hydra and Spetses, the Nemea wineries and even Athens are within reach. Further south, Monemvasia, Elafonisos and the Mani villages each fill a day.

Kefalonia's best day out is Ithaca, a short ferry ride from Sami, and in summer boats also run to Zakynthos and Lefkada. Beyond those, most outings stay on the island itself, and most crossings stop outside the warmer months.

Both work for a family beach vacation, and neither has theme parks, zoos or aquariums. On Kefalonia the gentle sandy beaches are in the south at Skala and Lourdas, and the Melissani boat ride and the harbour turtles make good treats.

The Peloponnese adds kids' clubs at the large Messinian resorts and shallow sand at Tolo and on Elafonisos. Mycenae and Olympia suit older children if you go early, before the heat. Either way, expect plenty of time in the car.

You need a car in both, but the Peloponnese is easier to cover. Motorways run from the Corinth Canal to Kalamata and along the north coast towards Olympia, although the Mani and the mountain roads are slow.

Kefalonia has no fast roads, so every trip across the island means winding ridge and cliff roads. Argostoli to Fiskardo takes about an hour and a half, and the buses run too rarely to be useful. The summer ferry from Argostoli to Lixouri is the one real shortcut.

Neither is a place to go for shopping, and in both the best things to take home are edible. Nafplio's old lanes give the Peloponnese the edge, with jewellery, worry beads and ceramics, along with weekly markets in Kalamata and Tripoli. Kefalonia has Argostoli's Lithostroto and the small boutiques around Fiskardo's harbour, and its best buys are Robola, thyme honey and mandoles.

The Peloponnese is the cheaper of the two, especially for village rooms in the Mani and Arcadia, though entry fees at the major sites add up. Kefalonia is mid-priced for a Mediterranean island: fair value around Skala and Lassi, noticeably dearer in Fiskardo and Assos. In both, a hire car is a cost you cannot avoid, and June and September cost less than high summer.

The Peloponnese has one outstanding event: ancient drama on summer weekend nights in the theatre at Epidaurus, where actors need no amplification. Kalamata also holds an international dance festival in July. Kefalonia's music is gentler and more local, with kantades serenades and Argostoli's philharmonic band at village festivals and open-air concerts in the squares. Outside summer, neither has much to see on stage.

Thermal water is what separates the two. Kefalonia has no bathing tradition, so pampering means the spa of a larger resort hotel around Lassi, Skala or Fiskardo. What it does well is calm: long lunches in hill villages, the quieter Paliki peninsula and evenings by the harbour in Assos.

The Peloponnese has the edge, with the old spa town of Loutraki, the springs of the volcanic Methana peninsula and the sulphur-fed lake at Kaiafas, as well as the most complete resort spas on the Messinian coast. Its stone villages and empty coves outside high season are just as slow-paced, so the springs come as an extra rather than the point.