In this work, we present a density functional theory benchmark on antioxidant-related properties for a series of six polyphenols that are well-known antioxidants: caffeic acid, cyanidin, ellagic acid, gallic acid, myricetin, and phloretin. Computations on the 24 O–H bond dissociation enthalpies (BDEs) and 6 ionization potentials (IPs) were performed using twenty-three exchange–correlation functionals combined with four different basis sets in the gas-phase, water, and methanol; calibration against the Domain-based Local Pair Natural Orbital CCSD(T) (DLPNO-CCSD(T)) approach was employed. Mean absolute deviation (MAD) as well as linear fitting results suggested the LC-PBE approach as the most suitable for O–H BDEs in the gas-phase. The LC-PBE, M06-2X, and M05-2X results presented the smallest MADs for O–H BDEs when compared to the reference, in water. The LC-PBE results had the smallest MADs for IPs in the gas-phase while M05-2X, M06-2X, LC-PBE, and LC-ωPBE exhibited the best results for MAD in water. We expect the outcomes from the present work will serve as general guidance for researchers working in the field.