My friend and I went to 3 cities; Sao Paulo, Manaus (for the amazon) and Rio de Janeiro. Rio was definitely our favorite! It had that city feel with the shopping and nightlife, but it also had the beach. The views of the city are also so beautiful from the beaches and mountains. I would 100% come back here.
Insider Tip:Rio is a little more pricey of a city in Brasil, but definitely worth it.