Two weeks in Brazil. Where should we go?

There's a lot to see in Brazil, but you should consider Rio de Janeiro (expensive, but unmissable), Ouro Preto (colonial charm and good food), Ilha Grande or Paraty (fun in the sun) and Foz do Iguaçu (perhaps the most impressive waterfalls in the world).

I would suggest that you combine Rio de Janeiro Foz do Iguaçu and and Paraty for a nice combin ation of culture, nature and nightlife and in two weeks it's doable to visit all 3 places as long as you are ready to use domestic flights to and from Foz do Iguacu.

Rio de Janeiro - sight seeing, nightlife
Foz do Iguaçu- impressive waterfalls
Pantanal (Cuiaba) -  Wildlife

Obviously, you have to go to Rio de Janeiro - nightlife, sightseeing, beaches, culture... I'd also add a couple of days at a party beach like Buzios, to round out one full week.

My suggestion for the second week would be to go to Salvador Bahia for three or four days. Salvador has a warmer climate, beaches, and lots of African-influenced food, dance, and culture. F Design Hostel is a neat place to stay. From there, if you want to see a more natural side of Brazil, you could spend a few days in Parque Nacional da Chapada Diamantina.