Costa Blanca or Formentera?

Both coasts have long stretches of sand, but Formentera's beaches are in a different class. Ses Illetes is a spit pointing towards Espalmador, with shallow, glass-clear water on both sides, and Llevant is the wilder side of the same strip. Migjorn gives you kilometres of dune with room to spare, and even Es Pujols, the most ordinary of them, is a good resort beach.

The Costa Blanca answers with variety and size: Benidorm's Levante and Poniente for children, the long strands of San Juan and Guardamar in the south, and clear coves such as Granadella and Portitxol in the north for snorkelling. The cost is crowded towels on the main beaches in high summer, and even the clearest northern coves rarely have the turquoise of Ses Illetes.

The Costa Blanca is the better place to eat, as long as you choose the town with care. Rice is at the heart of it, from arroz a banda by the sea to the egg-crusted arroz con costra of Elche. Dénia is known for its red prawns, Alicante's old town and Mercado Central make a proper tapas round, and Fondillón wine and turrón from Xixona add something local to take home.

Formentera's cooking is narrower. Grilled fish, lobster stew and the peix sec salad at a chiringuito above Migjorn make a fine long lunch. Beyond that there is no market, little street food and only a handful of good kitchens in Sant Francesc and Es Pujols, and many of those close outside the summer.

Neither is a place to go for culture, but the Costa Blanca at least fills a few good days. Alicante has the Castle of Santa Barbara and the MARQ, Elche has its UNESCO-listed Palmeral, and the white old town of Altea and the clifftop castle at Guadalest are worth the trip. The Hogueras and the Moors and Christians parades show local tradition at full strength in summer.

Formentera's sights fit into one afternoon between swims: the fortified church at Sant Francesc, the lighthouses at Cap de Barbaria and La Mola, a Bronze Age tomb and the outline of a Roman fort.

After dark the two are hardly in the same league. The Costa Blanca has Benidorm, one of the Mediterranean's big party resorts: loud, good-humoured and in no way stylish, with shows and dancing well into the small hours, and some of it carries on through the winter. Alicante's old quarter below the castle offers a more Spanish kind of night, with locals moving between terraces and small bars that only fill up late. The northern towns wind down after a long dinner.

Formentera's nights are short and belong to the summer. The main event is a drink at sunset on the west coast. Es Pujols has a small cluster of bars and a club or two, and the rest of the island goes to bed early so as to be on the sand in the morning. Anyone who wants serious clubbing goes to Ibiza, and the ferry back sets the end of the night.

The northern Costa Blanca is far more dramatic. The Peñón de Ifach rises from the sea at Calpe, Montgó stands over Jávea and the Serra Gelada forms sea cliffs. Inland, ranges climb above 1,500m with serious hiking, and the crags around Sella draw rock climbers from across Europe.

Formentera is flat and gentle, with pine scrub, salt pans and dunes. It is best seen by bicycle on its green routes, or underwater over the seagrass meadows, which make for superb snorkelling. Both have flamingos on salt lagoons, at Torrevieja and Santa Pola on the mainland and at Estany Pudent on the island.

From the Costa Blanca you have a real choice of outings. Valencia has its cathedral, silk exchange and City of Arts and Sciences. Closer by are the Borgia palace at Gandia, the castles of Xàtiva and Villena, Alcoy's bridges over the gorge and the boat to Tabarca, and from the southern resorts Murcia and Roman Cartagena are both within reach.

Formentera offers Ibiza, half an hour away by fast ferry, with the walled hilltop of Dalt Vila and its cathedral, plus a boat to the islet of Espalmador. After that the list ends.

With children, the Costa Blanca is much the better choice. Around Benidorm there is a theme park, water parks, an animal park and a marine park, all a short drive or bus ride away. The pools and waterfalls of the Fonts de l'Algar make a cool afternoon away from the sand. Add calm beaches and plenty of pool hotels and apartments, and there is enough to fill a long stay, even with small children.

Formentera has the sea and very little else for children. The shallow, sheltered water at Ses Illetes is ideal for paddling, and older children enjoy cycling between beaches. But nothing on the island is built for children, the beaches have little shade, and the flight to Ibiza and then the ferry make the journey harder with toddlers.

Arriving is simpler on the Costa Blanca, with Alicante airport within an hour of the main resorts and the slow, scenic coastal TRAM running north towards Dénia. Even so, the coves, mountain villages and theme parks really need a car.

Formentera always means a ferry from Ibiza to La Savina. Once you are there, the island is only about 20km long and mostly flat, so a bike, e-bike or scooter gets you around easily.

Neither is a shopping destination, but the Costa Blanca has more to offer. Alicante has high streets and a department store, Elche has shoe factory outlets, and the weekly markets in Jávea, Altea and Benidorm sell leather and ceramics.

Formentera's best is the summer artisans' market at El Pilar de La Mola, with handmade leather, silver and textiles, along with a few linen boutiques in Sant Francesc. For anything more, you cross to Ibiza.

The gap is wide. Benidorm and the resorts around Torrevieja are among the cheaper beach destinations in Western Europe, with plenty of apartments and set lunch menus. Only the northern towns of Jávea, Moraira and Altea push costs up.

Formentera is expensive at every turn. A small stock of rooms meets heavy summer demand, beach restaurants charge resort prices, and the ferry and vehicle hire come on top. Self-catering and the shoulder months help, but there is no cheap way to do the island in high summer.

Neither has much of a stage, but the Costa Blanca has a few things worth planning for. Alicante's Teatro Principal stages touring theatre and the ADDA has a season of orchestral concerts. Each August, Elche performs the Misteri d'Elx in its basilica, a sung medieval mystery play recognised by UNESCO.

On Formentera, live music means musicians at the La Mola market and sunset sets at a few beach bars, with no theatre or concert hall at all.

The two are level here, and in both the rest comes from the pace rather than from spas, with no bathing tradition in either. On Formentera the calm covers the whole island, which is low-rise and unhurried, with yoga and massage easy to find in summer.

On the Costa Blanca the quiet belongs to the northern coast around Altea and Moraira, which also has Arab-style baths in Alicante and health retreats in the hills. Benidorm and the busy southern resorts are not restful at all.