Attorney in BA said:
I've never been to the falls, but I have been told that the falls are in the Argentine side and the view of the falls is in the Brazilian side. Check this out before going, in case you make it there and miss the view.
No the better view of the falls is on the Argentine side. You can walk all through the falls, take a speedboat up to and almost under them. The Argentine falls are the ones that are in The Mission. The famous hotel is inside the Argentine side of the park.
However to compensate for their not so glorious view of the falls, the Brasilians have a lot of activities. We didn't bother going to the Brasilian side -- we did a 4WD trip on the Argentine side. Definitely do the speedboat thing.
You can also go to Paraguay on a boat trip from the city, it's supposed to be kind of cheesy, they do some dance to greet the boat or something.
You really don't need much time in Iguazu -- one day to see the falls, maybe one other day to do activities, ie the 4WD thing, ziplining, a trip to the Brasil side or Paraguay.
Apart from the one five star hotel, all accommodations are far away from the falls, so you need to go with an organised tour. The town itself doesn't have a lot to do, or it didn't 4 years ago, it may have changed by now. Most of the accommodations do have pools though so you can hang out there.
If it rains, the entire town floods pretty quickly and half the roads weren't paved when I was there so be prepared to get muddy!
If you've got time, the Jesuit ruins are supposed to be worth the trip, we didn't bother doing it, opted for spa and some cocktails instead, haha. It's a full day as well, if you're 4 people you might want to figure out prices of going with a tour versus renting a car between the four of you -- may be cheaper to do it that way.
Have fun -- the falls are really beautiful, but beyond them there's not a lot to do up there. No beaches, so you may want to go to the Esteros del Ibera (south west of Iguazu in Corrientes province I believe) -- I have not been but it is meant to rival Brasi's pantanal for birds and wildlife:
http://gorp.away.com/gorp/location/latamer/argentin/top_twenty14.htm
The other place to consider closer to BA on your way back would be PN Palmar, another national park on the Parana river, more accessible than Ibera.