Most Juiciest Cut! A long and lean muscle located within the Loin; Buff Tenderloin is the juiciest cut of beef. It is extremely multipurpose. Use a portion of it for a roast while slicing filet mignon from the end or cut the full loin into other pieces of steak. As a roast, the loin can be prepared in almost infinite dishes, depending on the spices and sauces, you use with the recipe.