Best quality grade given by the USDA. Prime is produced from young, well-fed beef cattle. It has abundant marbling and is generally sold in high-end steakhouses or butcher shops. Prime roasts and steaks are excellent for dry-heat cooking (grilling or roasting). Less than three percent of all beef qualifies as USDA Prime.
Just below Prime on the scale. Choice is high quality, but has less marbling than Prime. Choice roasts and steaks from the loin and rib will be very tender, juicy, and flavorful and are, like Prime, suited to dry-heat cooking. Many of the less tender cuts, such as those from the rump, round, and blade chuck, can also be cooked with dry heat if not overcooked. Groceries and restaurants most commonly advertise Choice.
Lower on the quality grade scale, Select is normally leaner than the higher grades. It is fairly tender, but, because it has less marbling, may lack the juiciness and flavor of the higher grades. Only the tender cuts (loin, rib, sirloin) are best for dry heat cooking. Other cuts should be marinated before cooking or braised to obtain maximum tenderness.
Marbling plays a big role in quality grades (as referenced above) because the more marbling you have, the more flavor. Marbling is the name for the white flecks of fat in the beef. Higher amounts of marbling also protect beef from overcooking and make the meat juicier. In turn, you are less likely to dry the meat out over high heat.