Hahaha ... I know. The poster shoulda used the search function, as much has been written here on the forum. But I would personally take the RT-PCR, even if options, because it is gold standard and I don’t follow the American lead on CoV matters. I also don’t know if the OP is going to USA specifically or may be inappropriately grouping the two test versions when most nations require RT-PCR. Additionally, not all antigen test versions are rapid. In fact, the CDC clearly delineates the turnaround range for both versions, antigen or NAAT (umbrella for RT-PCR) as 15 minutes to 3 days because there are so many approved variations on the market.
In the unlikely event a flight is diverted and lands elsewhere, also best to have the version universally accepted.
I don’t know if tips for finding viral antigen test centres have been provided here. Or if such a version is offered at the airport. But Google search ‘coronavirus teste antígeno São Paulo’ should bring up several options. Be mindful that hundreds of CoV tests are ANVISA-authorized and, again, some antigen tests go to a lab (ie, not rapid) in the same way that NAAT formats are sent to a lab.
Parenthetically, I think the USA FDA will grant EUA to the Johnson&Johnson vaccine tomorrow. Yet 1 in 4 infections at the study’s primary endpoint occurred in the vaccine group.