This paper compares ADCC, ADCP, CDC, FcγR binding, C1q binding and FcRn binding across five practical dimensions: biological mechanism, assay architecture, endpoint interpretation, critical controls and appropriate use in candidate selection. It also presents a tiered testing workflow for programmes that seek effector-enhanced activity, deliberately attenuated Fc engagement or more informative evidence for an ambiguous result. The guiding rule is simple: select the endpoint that directly tests the intended biological decision, then use orthogonal assays to explain that endpoint.