What type of broccoli is most nutritional? It's not the regular variety, but rather broccoli rabe (or raab as it is sometimes referred to). If you compare the antioxidant content of each, the rabe's ORAC value is over 2x as high as regular broccoli.
Is cooked broccoli less nutritious than raw? With the rabe, the ORAC decreases by about 50% when it is coooked. With your typical common broccoli, the ORAC value actually increases by about 33%. But make no mistake about it, the act of boiling or cooking is not creating new antioxidants nor is it enhancing the bioavailability of them. Rather, there's a much simpler explanation for this discrepancy. When cooked, much of the water content from the vegetable evaporates, which leaves you with a denser concentration of the vegetable and everything in it, including the antioxidants. Fortunately too, unlike most veggies, the types of antioxidants in broccoli are not greatly affected by the heat of cooking (contrast that to others, which see their nutrients destroyed to some degree by the heat).
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