I am seeking recommendations for SIM cards for next week's trip to Rio:

1) a pre-paid SIM card with voice/text/data for an unlocked iPhone 4S for 2 week usage

2) a contract SIM card with voice/text/data for an unlocked iPhone 4S

3) both a pre-paid and a contract data-only SIM card for a Huawei E355 Unlocked GSM 3G 4G HSPA+ 21.6 Mobile Broadband Hotspot Router Modem

Which carrier works better? Oi, Tim, Claro, or Vivo? Also, in case there's little or no difference in the quality of service, which one is cheaper?

-tia ^