round is indeed lean. So are tenderloin (in pork as well as beef) and flank steak (also known as skirt steak). Tenderloin is pricey, though and can be tricky to cook (gets tough quickly) because there's not much fat in it. Unless you're an experienced cook, I wouldn't start out cooking tenderloin. Nice to order in a restaurant, though. This cut is often served as "medallions."