Do not worry and fly whatever takes you there. I would get scared only in minor lines in jungle areas on board crappy props or so. But São Paulo and Iguaçu are served by all the major companies hundreds of frequencies every day.
If I could advice you on wich company to avoid, it would be Viação Aérea Rio Grande, that's to say, VARIG, for two reasons: 1.-they are the most expensive and 2.-some of their employees consider themselves the top of the world and thus "exhaust" some kind of "cold superiority" feeling "against" the passengers
Enjoy your trip and...