Parkinson’s disease (PD) affects 10 million individuals worldwide with no available disease modifying therapies. The pathological hallmark of PD, Lewy bodies, are characterized by aggregated α-synuclein (α-syn) inclusions in disease lesions. In preclinical models, aggregation of α-syn leads to neuronal dysfunction, cell death, and propagation of Lewy pathology. Six clinical stage α-syn targeting monoclonal antibodies that were developed to treat or slow the progression of PD have advanced into efficacy trials, but none to date have achieved their primary endpoints. Except cinpanemab, which binds the N-terminus of α-syn, all other clinical α-syn antibodies bind C-terminal epitopes. To evaluate the impact of binding characteristics on functional activity, we affinity matured cinpanemab and benchmarked it against the clinical antibodies that vary in their affinity and selectivity for aggregated forms of α-syn. Our evaluation shows the impact of epitope, affinity, selectivity, and assay format on PFF uptake, and PFF-seed induced aggregation and S129 phosphorylation of endogenous α-syn in cellular models of PD. The comparative assessment provides new insights into the properties of α-syn antibodies and should aid in the design of next generation therapeutics for the treatment of PD and other synucleinopathies.