An antioxidant can act through different  mechanisms, and those tests should uncover partially the type of antioxidants contained in  your samples, for example a sample could show strong scavenging activity  but low iron chelating capacity which means that  the  sample's antioxidant molecules do not act as chelators or through chelating. Generally speaking ABTS and DPPH could give you an idea  about your  samples total activity  but performing the other tests could add more information.

I fully concur with the above answers. No single assay can be regarded as the benchmark for the assessment of antioxidant capacity as each assay has its own limitations. Therefore I recommend that several antioxidant assays are used to give an overall picture of the antioxidant capacity of a sample. I suggest Total Phenol Content, FRAP, DPPH and Ferrous Ion Chelating Assay.