I really thought the argentinian side of Iguazu falls was really beautiful, better than the brazilian side, but I guess you gotta see both. If you go to the falls, I'd put an extra-day to see the Itaipu hydroelectric power plant, if you have the opportunity to see Sao Paulo and Rio de Janeiro, these two urban environments are amazing and will give you a different sight on Brazil, in Uruguay, after my trip, I'd tell you to go to Montevideo and spend a couple days there, than go to Punta del Este, and save a day for going to the beach there, I have not been to Colonia but I guess it is a really nice place. =)