The Iguazú Falls are right on the border between Argentina and Brazil; if you're traveling from Buenos Aires, your best bet is to fly to the town of Iguazú and visit the falls from there. You can also arrive at Iguazú Falls from the Brazilian side by landing at Foz do Iguaçu, the closest Brazilian city.
This weeklong itinerary gives you a chance to explore Buenos Aires before heading on to the falls, and this 10-day tour gives you a chance to combine wine tasting, trekking, and sightseeing as you travel through Buenos Aires, Bariloche, Mendoza, and finally, Iguazú Falls.
From Buenos Aires
Duration: 2 hours, plus travel to/from airports
Visiting Iguazú Falls National Park from Buenos Aires is easy, as several daily flights connect the Argentine capital with the popular tourist destination. Most flights leave from Buenos Aires' Aeroparque (AEP) airport, which you can easily reach by taxi or private transfer. Aerolineas Argentinas also operates some direct flights from Ezeiza International Airport (EZE), which are convenient if you're arriving from an international destination and want to continue on directly to Iguazú.
Duration: 1.5 hours from São Paulo, plus travel to/from airports
If you want to reach Iguazú Falls from Brazil, your best bet is to fly to Foz do Iguaçu International Airport (IGU) and visit both the Brazilian and Argentine sides of the falls from there. The airport is only a five-minute drive from the Brazilian side of the falls and around 35 minutes away from the Argentine side. You will have to cross the border to reach the Argentine side, so don't forget to bring your passport.