You can purchase TAM's Brazil Pass even if you take AA into Brazil. All TAM flights will earn you AAdvantage miles (whereas I believe you will not earn UA miles on Varig's shuttle between Sao Paulo Congonhas and Rio Santos Dumont). TAM has the best domestic service in Brazil, meals and alcohol are served on flights of any duration. GOL is a pretty good airline too, but no inflight meals and less frequencies compared to TAM and Varig.