Over Christmas we spend four nights staying and visiting Iguazu falls. The falls sit right on the border of Brazil, Argentina and Paraguay although we did not visit Paraguay. As we stayed for four nights we decided to stay on the Brazilian side just because they had more options of hostels and its a bigger city than Puerto Iguazu. We arrived by plane into Puerto and got a taxi from there over the border through the passport checks and into Foz do Iguacu. It was really easy and the prices for taxis are set at the airport.
We stayed at concept hostel which was pretty nice and has a pool so would recommend staying here for sure.
Getting to the falls is pretty easy there are buses and also lots of taxis to get you there. If you are staying in Foz do Iguazu getting the bus is very easy and cheap it goes along the main road and stops right outside. You can also get the same bus to the bird park and the airport. Cost is 3,45 R. Getting to Argentina is a bit more difficult and involves a couple of buses as you have to stop and get out at the border for both Brazil and Argentina so takes a bit longer.
For Brazil allow yourself about 2 hours there, this side gets a bad rep but I actually liked it better. Amazing view of the whole size of the falls and you get to walk out to the devils throat and get really close to the action.
Argentina allow for a whole day and a lot of walking. Take sunblock as it is really hot! This side is beautiful and much much bigger. Pack a lunch as the food options are not that great and pretty expensive.