Instant oatmeal has an amount of antioxidants which is comparable to quick-cooking and old-fashioned oatmeal. Even though oats have an ORAC value comparable to many other grains, antioxidants isn't the only reason to consume them. There are numerous studies suggesting oatmeal may be beneficial for weight loss, as subjects who ate it were found to eat less of it, relative to more processed grains like corn flakes and breads.
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