Foz do Iguacu or Rio de Janeiro?

This is the widest gap between the two. Foz lies deep in the interior. The nearest swimming is at lake beaches on the Itaipu reservoir, half an hour or more away by car, so most visitors swim in the hotel pool.

In Rio the sea is at the end of the street. Copacabana, Ipanema and Leblon are within walking distance of the hotels, and Prainha and Grumari further west have surf and cleaner, quieter sand. On the open beaches, swim near the lifeguard posts, and leave the beaches inside the bay for looking at.

Neither is a city to visit for food alone, but Rio offers more. Foz has the churrascarias and pay-by-weight buffets found across Brazil. What sets it apart is the esfihas and kibbeh of its Lebanese community, and an evening of grilled meat and Malbec across the bridge in Puerto Iguazú.

Rio adds the boteco, a neighbourhood bar with draught beer and plates of pastéis to share. It also has Saturday feijoada, juice bars on the corners, snacks and caipirinhas from beach vendors, and modern restaurants in Leblon, Ipanema and Botafogo.

Foz has a few unusual and memorable sights rather than a full cultural programme. There is the tour inside the Itaipu dam, the white-domed mosque and the Buddhist temple looking towards Paraguay, and the obelisk where three countries meet. There is no old town.

Rio fills several full days. Christ the Redeemer and Sugarloaf come first. Then there is the gilded São Bento monastery, the Real Gabinete Português de Leitura reading room, the museums on Praça Mauá, and the walk through Santa Teresa down to the Selarón steps.

Foz goes to bed early. There is a short strip of bars and terraces in the centre, a few clubs at weekends and casinos across the borders, and most visitors have been out at the falls since early morning.

In Rio, going out starts late and happens largely on the street. Crowds gather under the Lapa arches, Botafogo's bars spread across the pavements, Leblon has smarter cocktail bars, and before Carnival the street parties called blocos take over whole neighbourhoods. Take taxis between districts after dark.

Both are outstanding, but in very different ways. Foz is one overwhelming sight. Some 275 cascades fall through the rainforest, seen from the cliff-edge walkway on the Brazilian side and the trails to the Devil's Throat on the Argentine side, with boats into the spray and toucans and coatis close by.

In Rio, nature runs through the city itself. There is the Tijuca forest, short steep climbs up Dois Irmãos and Pedra da Gávea, hang-gliding down to the sand at São Conrado, and surf at Arpoador. Rio gives you more variety, and Foz gives you the bigger spectacle.

From Foz, the day trips are border crossings: to Puerto Iguazú and the Argentine side of the falls, and to Ciudad del Este for shopping. The Jesuit missions are too far for a day out.

Rio has more choice. Petrópolis, where the emperors spent their summers, is up in the hills. A ferry crosses the bay to Niterói for the Niemeyer museum and the view back. Inland there are quiet old coffee towns. Paraty and Ilha Grande are better as overnight stays.

Foz is the easier family trip, even with young children. The main walkway on the Brazilian side is short and gentle, with a lift at the end, and the roar of the water and the coatis on the path keep small children happy. The walk-through aviaries of the bird park are right by the park entrance, and older children can add the boat ride into the spray and the tour inside the Itaipu dam. The tiring parts are the car journeys between sights, the border queues and the summer mosquitoes.

Rio takes more effort with children, and the trip is built around the beach. Younger swimmers are better off in the calmer water at Leme, Praia Vermelha and Barra. The Sugarloaf cable car, the cog railway up Corcovado, AquaRio and the BioParque zoo fill the other days. Heavy traffic, uneven pavements and the need to watch your belongings make it hard going, and there is no theme park to fall back on. Summer heat is tiring for children in both cities.

In both cities you ride more than you walk, and in Foz a little more so. Its small centre is walkable, but the falls are 20km out on a direct bus, Itaipu is across town, and the Argentine side usually means a taxi or transfer through two border posts.

Rio's metro runs straight through the districts visitors use, from the centre to Leblon, and the beachfront is flat and easy on foot. Santa Teresa, Tijuca and the western beaches still need a taxi, and traffic through the tunnels can be slow.

In Foz, shopping means bargain hunting across the border, in the crowded discount galleries of Ciudad del Este and the duty-free shops. In town there is little beyond a mall and gemstone souvenirs.

Rio has things worth buying in their own right. The boutiques of Ipanema and Leblon sell Brazilian swimwear, linen and resort clothes. There is also the Sunday hippie fair in Ipanema and the cheap fabric and Carnival costume streets of Saara downtown.

Day to day, the two cost about the same, with cheap buffet lunches and inexpensive ride-hailing in both. Where the money goes is different.

In Foz, rooms and meals are cheap, but park entry, boat rides, the bird park and the Itaipu tours soon add up. In Rio the beaches and forest trails are free, but hotels near the sand are expensive, and much more so around Carnival and New Year.

Foz offers little beyond dinner shows of Latin American folk dance put on for tour groups.

Rio has samba most nights: in Lapa's old houses, at neighbourhood rodas de samba, where musicians play around a table, and at the samba schools' rehearsals before Carnival. There are also small bossa nova venues, and opera and ballet at the Theatro Municipal.

Neither city has a spa or bathing tradition, so in both, relaxing mostly means your hotel or the outdoors. In Foz that means a resort hotel on the falls road, with a pool and gardens for a rest day between sights.

In Rio it means the sea, yoga on the sand and an evening walk along the promenade or around the lagoon. For real quiet, go up into the cooler hills of Santa Teresa.