I try to keep English on the ATC, but more then often get the other side answering or calling me on Portuguese, I guess by the principle of "Brazilian Callsign", should handle this. The worst Controllers are certainly in Rio, arogant and dismotivated to speak English. Many times they seem to ignore your call and get Portuguese speaking AC served first.
@Hurz: You'll be flying to SBEG next as well, right? This way you"ll have to deal with all Brazilian regions... FIR Amazonico may be bad radio quality, but controllers are more used to US traffic...