Taekwondo is my "wild" guess, but it could be Shooting.
I would like to think that Brazil will be THAT good, but I just don't see it, simply because we aren't a top sport nation like previous hosts. The best comparison for us is Greece, I think. They went from 13 medals (4G 6S 3B) in Sydney to 16 (6G 6S 4B) at home. Similarly, Brazil will improve from London, but not that much. I expect 7 medals more than the 17 we achieved in London, and 2/3 more golds.