Grapes are often touted for their resveratrol content, but between black versus red grapes, you will get more with the latter. Or better yet, just eat a handful of peanuts if you want more total antioxidants and resveratrol.
ORAC Source
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010