Madrid or San Sebastian?

This is the starkest difference between the two. Madrid sits on the central plateau with no coast within a day's reach, so summer cooling-off means municipal pools or the reservoirs under the Sierra de Guadarrama.

San Sebastian has one of Europe's great city beaches in La Concha, a sheltered bay of pale sand a few minutes' walk from the old town, with quieter Ondarreta beside it and Zurriola facing the open Atlantic for surfers. The catch is the Bay of Biscay: the water stays cool and the swimming season is really just high summer.

Both are among Spain's best places to eat, but San Sebastian has the edge. Madrid's strength is breadth. You can work along the tapas counters of Cava Baja, try cocido and calamari sandwiches, and eat the whole country's cooking, from Galician seafood to Basque grills, with plenty of high-end tasting menus too.

San Sebastian is narrower and more intense. The pintxo bars of the Parte Vieja and Gros each have a speciality and serve it with txakoli, there is a remarkable concentration of acclaimed restaurants for a city this small, and the cider houses of Astigarraga open from January. If eating is the point of the trip, this is where to go, provided you are happy with Basque food at nearly every meal.

Madrid is in another league for art. The Prado, Reina Sofía and Thyssen-Bornemisza line one boulevard and can fill several days, and the Royal Palace, Plaza Mayor and the Goya frescoes in San Antonio de la Florida add a grand Habsburg and Bourbon backdrop.

San Sebastian is better enjoyed as a townscape than as a list of sights: the rebuilt grid of the Parte Vieja, the Basilica of Santa Maria, the Miramar Palace above the bay. The San Telmo Museum and Chillida's Peine del Viento on the rocks at Ondarreta are the highlights, and two or three days see it all.

Madrid is built for going out late. Clubs open around two and run past dawn, and each district has its own crowd: rock and indie in Malasaña, the gay scene in Chueca, terraces in La Latina and Lavapiés, big clubs around Gran Vía and Sol.

San Sebastian's best nights are early and food-led, hopping between pintxo bars in the old town until late. Beyond that there are only a few late bars and clubs, and the city livens up properly mainly in summer and during Semana Grande in August.

San Sebastian has the outdoors on its doorstep. Monte Igueldo, Urgull and Ulia frame the bay, and the coastal path from Ulia to Pasaia and on over Jaizkibel to Hondarribia runs along cliffs and sandstone formations. Surfing, kayaking and paddleboarding are all easy in town.

Madrid's green spaces are city parks such as the Retiro, Casa de Campo and Madrid Río. For real hiking you go an hour north to the Sierra de Guadarrama, which has higher granite peaks, the boulders of La Pedriza and some winter skiing, but it is a separate outing rather than part of the city.

Both make excellent bases, and Madrid is the stronger one. High-speed trains reach Toledo and Segovia in about half an hour, and walled Ávila, Salamanca and Cuenca are not much further, so a week can take in a run of historic cities that Madrid itself lacks.

San Sebastian's outings are more varied in kind than in depth. You can choose between the Guggenheim in Bilbao, walled Hondarribia, the French Basque coast at Biarritz and Saint-Jean-de-Luz, and the Rioja Alavesa vineyards, though most of them are reached by bus or road rather than fast train.

Both are easy with children, and in both they stay out in the squares late in the evening. What differs is the kind of day out. Madrid offers parks and attractions: rowing boats in the Retiro, the zoo, aquarium and funfair in Casa de Campo, and theme parks further out, all made harder by July and August heat.

San Sebastian's draw is sheltered beaches in the centre, plus the harbour aquarium, the Eureka science museum and the funicular to the old funfair on Igueldo. Rainy spells can wipe out beach days, and after a few days families tend to run out of things to do in town.

Neither city needs a car, but they work differently. Madrid's centre walks well from the Royal Palace to the Prado, and its large, air-conditioned metro runs to the airport and to Atocha and Chamartín for the fast trains.

San Sebastian is small enough to cross on foot in under an hour along the bay, with bike lanes on the waterfront, buses for the outer sights and Euskotren to the French border and towards Bilbao.

Madrid is far the better shopping city. Luxury houses line Calle Serrano in Salamanca, the flagships and department stores cluster on Gran Vía and Preciados, and independent and vintage shops fill Malasaña, Chueca and Conde Duque. On Sunday mornings there is El Rastro.

San Sebastian has pleasant boutiques in the Centro, surf shops in Gros and Basque goods such as espadrilles and berets in the Parte Vieja. The best souvenirs are edible: Idiazabal cheese, txakoli and preserved anchovies from La Bretxa.

The real gap between these two is in the room rather than on the plate. A Madrid hotel is priced like one in any large capital and climbs only around big events, so for most of the year the cost of a bed is steady and leaves more of the budget for the city itself.

In San Sebastian the bed is where the money goes. Rooms are few for the demand, and in July, August and festival weeks they reach the levels of Europe's dearest capitals. Food narrows the difference less than you might hope: a careful pintxo evening stays reasonable, but a long one adds up, and the celebrated tables in the hills are a splurge in any season. A visit in spring or autumn closes much of the gap, and the bay, the beaches and the cliff paths are free all year.

Madrid has a stage scene all year round. There is opera at the Teatro Real, the national orchestra at the Auditorio Nacional, zarzuela, long-running musicals on Gran Vía, and flamenco every night in tablaos where the best performers are serious artists. Jazz clubs and indie venues in Malasaña fill in the rest.

San Sebastian's music is concentrated in summer, with Jazzaldia in July, including free concerts on Zurriola beach, and the Quincena Musical in August. Outside those weeks the Kursaal and the Teatro Victoria Eugenia keep a modest programme going.

San Sebastian is the more restful of the two. It has a real seaside spa tradition in the old bathing pavilion on La Concha, which offers seawater pools and treatments looking onto the bay, and the city's calm pace and evening walks on the promenade help too.

Madrid is loud and late by nature. Relaxation there means one of the Arab-style bathhouses in the old centre, a hotel spa or a slow afternoon in the Retiro or the Botanical Garden.