Which type of tomato has the most antioxidants? In their report, the USDA only provided antioxidant content (ORAC values) for two kinds of fresh tomatoes: plum and red ripe. Between those two, the plum is 41% higher than red ripe. All varieties are a rich source of lycopene which is one of the few phytonutrients which does not degrade when heated. In fact, lycopene becomes more bioavailable for absorption after it is heated.
The USDA probably didn't test heirloom because there are so many variations, it would be near impossible to establish a standard value which would be good guidance for that category. That being said, we would predict heirloom tomatoes would test as having more antioxidants than the conventional cultivated tomato species. Based on the patterns seen in other fruits and vegetables, we would predict the darkest heirloom varieties to be the kind with the highest amount of antioxidants and those are: Cherokee purple, black pear, black Russian, purple Russian, brandy wine, canistrino, and Japanese. Why? Because those with the purple shades have been shown to have higher levels of anthocyanins.
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