Go to Rio for one or two nights to see the sites then get the fuck out of there, even non carioca Brazilians know this. I lived in Florianopolis for a while and it was beautiful, clean, safe, etc but then it's their San Francisco, rich tech types.
I visited Rio a few times and hated the place, big south American cities are dangerous fucking places to be, especially if you are obviously a gringo and don't speak the language. In fact don't bother with Brazil or Argentina at all, Chile and Peru are both much nicer places in general if you're in South America.