Since i read many are interested in Brazil and Argentina (And im familiar with both countries), i must say i like argentina over brazil.
Brazil = Some good places (florianopolis, camboriu, Rio if you dont get killed, Sao Paulo) , "ok" food (Churrasquerias) and good beer. Kinda cheap (forget about buying imported stuff)
Argentina = Buenos aires is just a GREAT place to go and eat for some serious CHEAP money. You guys dont realize how great is. Downtown is kinda dirty but that wont ruin your day
. There are some GREAT restaurants, like CABAÑA LAS LILAS, where you can probably eat the best meat in the world, im talking about a 450gr steak, bloody, perfectly cooked by argentinian "parrilleros", or go to "Siga la vaca" and for us$15 or so, eat as much meat as you can (and its not some cheap ass meat).
So many nice places over there, and the nightlife, oh man, it start at 3 am in the morning and end at 10 am or so
so be ready for some serious clubbing.