Buenos Aires or Foz do Iguacu?

Neither is a beach destination. Buenos Aires lies on the Río de la Plata, which is too silty and polluted to swim in. The Costanera is for strolling and lying on the grass, and the Atlantic resorts such as Mar del Plata need a separate stay of several days.

Foz do Iguaçu has the slightly easier swim: lifeguarded lake beaches along the Itaipu reservoir, half an hour to an hour away by car, with warm water in summer. In both cities, the realistic choice on a hot afternoon is the hotel pool.

Buenos Aires is much the better place to eat. Its parrillas grill every cut over wood and charcoal, the Italian heritage brings thick pizza, fresh pasta and excellent ice cream, and the grand coffee houses on Avenida de Mayo let you sit for hours. Palermo has the most ambitious modern kitchens.

Foz offers rodízio at the churrascarias, buffets where you pay by weight, and good Lebanese esfihas and kibbeh, and you can cross the bridge to Puerto Iguazú for an Argentine grill. It is pleasant enough, but there is little fine dining, and many restaurants near the falls cater to coach groups.

In Buenos Aires the streets themselves are the attraction. There are the boulevards and mansard roofs running from the Plaza de Mayo past the Palacio Barolo to Congress, the marble mausoleums of Recoleta Cemetery, and serious art at the Bellas Artes and MALBA.

Foz has no old town and only small museums, but what it has is unusual. You can tour the inside of the Itaipu dam, visit a large mosque and a Buddhist temple that reflect its Arab and Chinese communities, and see the obelisk where three countries face each other across the rivers. A day covers it.

This is where the two differ most. Buenos Aires keeps famously late hours, with cocktail bars behind unmarked doors in Palermo Soho and Hollywood, electronic clubs that run past sunrise, and milongas in San Telmo where people dance until the small hours.

Foz has a short strip of bars and terraces that is busiest at weekends with local students, a few late clubs, and casinos across the borders. After a day on the trails at the falls, most visitors settle for a long dinner.

Here Foz do Iguaçu is in another league. The falls spread across nearly 3km of river in protected rainforest. A cliff-edge walkway on the Brazilian side gives the great panorama, and trails on the Argentine side lead right to the Devil's Throat. On top of that come boat rides, rafting, and coatis and toucans along the paths.

Buenos Aires sits on flat pampas with no hills within reach. Its green spaces are the Bosques de Palermo and the Costanera Sur wetland reserve, and the best escape is the Paraná Delta, explored by launch or kayak from Tigre.

Buenos Aires has far more to go out for. A fast ferry reaches the cobbled UNESCO old town of Colonia del Sacramento in Uruguay. Closer by are the delta town of Tigre, the gaucho silversmiths of San Antonio de Areco, the basilica at Luján and the planned city of La Plata.

From Foz the options end at the borders. There is Puerto Iguazú, usually combined with the Argentine side of the falls, and the discount markets of Ciudad del Este. The Jesuit mission ruins are three hours or more away, and border queues eat into any outing.

Foz is the easier place with children. The Brazilian walkway is short and gentle, the spray and the coatis keep them gripped, and the Parque das Aves lets them walk among macaws and flamingos. Resort hotels with pools make a calm base, though heat, mosquitoes and car journeys need planning.

Buenos Aires welcomes children everywhere, with pedal boats and the planetarium in Palermo and the Museo de los Niños for wet days. Long distances, broken pavements and dinners after ten are harder on young ones, and both Temaikèn and the amusement park at Tigre are an hour out.

Buenos Aires is the easier city to get around without a car. The flat grid makes each district walkable, the Subte links the centre with Palermo, buses run everywhere day and night on a single card, and taxis are plentiful. The catch is the long distances between neighbourhoods.

The centre of Foz is compact, but the sights are elsewhere. The falls lie about 20km out, Itaipu is on the other side of town, and reaching the Argentine park usually means a taxi or transfer through two border posts. Expect several car journeys on even a short stay.

Buenos Aires has things worth taking home: Argentine leather from the workshops of Villa Crespo, independent designers along the leafy streets of Palermo Soho, antiques and tango records at the Sunday fair on Calle Defensa, and the painted domes of Galerías Pacífico.

Shopping from Foz means bargains rather than style. Most of it is electronics and perfume in the crowded galleries of Ciudad del Este across the bridge, where fakes are common, plus duty-free shops, a mall and gemstone souvenirs.

Foz is the cheaper place day to day, with inexpensive mid-range hotels, buffet lunches, churrascarias and affordable rides to the falls. The catch is the sights. Park entry for foreigners on both sides, the bird park, the Itaipu tours and the boat rides all add up over a packed few days.

Buenos Aires can be good value at its neighbourhood parrillas, on its cheap public transport and for wine. Palermo, Recoleta and Puerto Madero, though, charge like a European city. In both places, the Argentine exchange rate can change what you pay from one trip to the next.

Buenos Aires is one of the great performance cities of the Spanish-speaking world. The Teatro Colón stages opera, ballet and symphony concerts in celebrated acoustics, and Avenida Corrientes is lined with theatres. Tango is danced for real in milongas with live orchestras, alongside folk peñas and jazz.

In Foz, the main evening entertainment is a dinner show of Latin American folk dances put on for tour groups. There is no orchestra or live music scene worth planning around.

Neither city is built for unwinding, and in both the spas are in hotels. In Buenos Aires the restful moments come from local habit: lingering over coffee, the long sobremesa after a meal and quiet Sunday mornings, all set against loud traffic and nights that run until dawn.

In Foz, rest comes from where you stay. The resort hotels on the falls road, with their pools, gardens and spas, make an easy recovery day between early starts on the trails.