Costa del Sol or Formentera?

Formentera has the finer beaches by some distance. The white sand of Ses Illetes, with clear turquoise water on both sides of the spit, and the long dunes of Migjorn are a different class from the grey-gold, fairly coarse sand of the mainland. The sea there is also a few degrees warmer in August.

The Costa del Sol's strength is quantity and convenience. It has an almost unbroken run of sand from Nerja to Estepona with sunbeds and chiringuitos, city beaches in Málaga, and clearer snorkelling coves around Maro. Expect crowds at Torremolinos and Fuengirola in high summer.

The Costa del Sol eats far better and offers much more choice. Málaga's old taverns pour wine from the barrel, the Atarazanas market sells fish and fruit, espetos are grilled on the beach at El Palo, and Marbella has fine dining. The resort seafronts are the weak spot, with menus aimed at foreign visitors.

On Formentera, the meal to have is a long seafood lunch above the water, with island dishes such as ensalada payesa made with sun-dried fish, and flaó for dessert. Beyond the beach restaurants there is little: no market life, uneven quality, and many kitchens shut out of season.

Here the gap is wide. Málaga alone has the Alcazaba above its Roman theatre, the Gibralfaro walls, the unfinished cathedral and a run of museums from Picasso to the Pompidou. Further along the coast are Marbella's whitewashed old town and the Nerja cave.

Formentera offers the fortified church in Sant Francesc, a Bronze Age tomb, the outline of a Roman fort and lighthouses at Cap de Barbaria and La Mola. You can see all of it in one day between swims.

The Costa del Sol has the far bigger night out, and in several styles. There are beach clubs and late clubs at Puerto Banús, the long-established gay scene in Torremolinos, cheap bar strips in Fuengirola, and tapas crawls in Málaga that keep going all year.

Formentera's evenings are sunset drinks on the west coast and a few bars in Es Pujols in summer. Anyone wanting real clubbing has to take the ferry to Ibiza and keep an eye on the clock.

Mountains give the Costa del Sol the edge outdoors. The Río Chíllar gorge above Nerja, La Concha behind Marbella, the Sierra de las Nieves and the Caminito del Rey all offer proper hiking within an hour of the beach.

Formentera is low and gentle instead, with salt pans, dunes, juniper scrub and flamingos in the Ses Salines park. The La Mola cliffs are its only height. Outdoor life there happens on and under the water, snorkelling and kayaking over the seagrass, and on a bicycle.

Few coasts in Europe beat the Costa del Sol for day trips. The high-speed train from Málaga reaches the Mezquita in Córdoba in about an hour and Seville in two, and the Alhambra is a drive away. Ronda, Antequera, the white villages and Gibraltar fill the rest of a week.

From Formentera the choice is Ibiza, half an hour away by fast ferry, for Dalt Vila and the villages, or a boat to the empty islet of Espalmador. After that, the island is the whole trip.

The Costa del Sol is built for children in a way Formentera is not. Between Torremolinos and Fuengirola there are pool complexes, gently sloping beaches, a zoo, an aquarium, a marine park, water parks and a cable car, so there is plenty to break up the beach days.

Formentera works for families who want only the beach. It has calm shallows at Ses Illetes, a small and safe island, and flat cycle routes for older children. There is nothing made for children, though, shade is scarce, and the extra ferry from Ibiza is a nuisance with toddlers.

Arrival is simpler on the Costa del Sol, where a commuter train links the airport with Málaga and the main resorts, although beyond Fuengirola you depend on slow summer buses or a car. Formentera takes a flight to Ibiza and then a ferry. Once you are there, the island is about 20km long and flat, so a hired bike or scooter gets you everywhere.

Shopping is a real activity on the Costa del Sol. There are luxury fashion houses on the harbour at Puerto Banús, boutiques in Marbella's old town, Spanish chains along Calle Larios and malls by the motorway.

Formentera has a handful of linen and jewellery boutiques in Sant Francesc and the craft market at El Pilar de La Mola. The market is a charming place to buy handmade leather and silver, but it is small.

Neither is cheap, but the Costa del Sol gives you far more ways to control costs. Marbella is expensive, yet the package resorts between Torremolinos and Fuengirola have plenty of mid-range rooms, and fish grills and tapas are fair value.

Formentera has few beds, high summer demand and resort prices at the beach restaurants, with the ferry and a hire vehicle on top. Self-catering and the edges of the season help, but there is no budget way to spend a summer week there.

Neither is a destination for performance, but the Costa del Sol at least has Málaga. The Teatro Cervantes stages the city orchestra, opera and dance, the peñas hold weekend flamenco, and big open-air concerts run around Marbella in summer. Formentera has musicians at the La Mola market, sunset sets at a few beach bars and no theatre at all.

The Costa del Sol has more to book. There are large spa hotels and detox clinics around Marbella, golf resorts with spas, and Arab-style baths near Málaga's old town.

On Formentera the calm itself is the treatment: a low-rise island with no big resorts, a few small hotel spas, and yoga and massage in summer. For quiet, it rivals Nerja or the hill villages, but for proper treatments the mainland wins.