The RT-PCR test identifies the virus’ genetic material, whilst the RTK-Antigen test identifies specific protein from the virus. The RT-PCR test has a higher accuracy compared to the RTK-Antigen test and is considered a gold standard test for the diagnosis of COVID-19.
You may do the RTK-Antigen which is less sensitive but the results will be ready within the same day. Do note that a negative RTK-Antigen test may still require a RT-PCR test for confirmation at the discretion of the Doctor.