The flight from Buenos Aires to the airport in Puerto Iguazu is only about an hour, and there are hotels of all price ranges near (or in) the Iguazu National Park. I bought an Iguazu Falls package trip that included airfare, overnight in a hotel, and a private guide for 2 days. This worked out well since the 2 days provided the opportunity to view the falls from both Brazil and Argentina. Having a knowledgeable guide to drive and facilitate the border crossing made the visit even more enjoyable.
American tourists will need to get a Brazilian Visa before leaving home, so don't plan to visit Brazil without one. The best panoramic views of Iguazu Falls are from Brazil, but an overnight trip to only the Iguazu National Park in Argentina is worthwhile.