Prime beef is the highest-quality, tenderest, most richly marbled meat from a small percentage of cattle. Ultimately, about 2 percent of American beef makes the cut and is stamped USDA Prime. Most prime meat goes to high-end restaurants. Only a few retail sources, mostly in major cities - Philadelphia included - and online/mail-order sources sell prime beef to the public. Many butchers will custom-order it. Prime beef and branded products of near-prime quality are available at Wegmans and Whole Foods markets. Branded beef is typically at the high end of its designated grade level. Unless labeled prime, that's Choice or,...