sirloin maybe? i don't know much about cuts of beef. i know when i get ground beef i get ground sirloin as it has the least fat. i don't buy steak so i know zilch about it.
Just think of it this way. The less the cow uses it the less connective/fat the cut will have. Hind quarter cuts tend to be leaner but the tenderloin (filet mingon if cut into steaks) is the most tender. However, it is flavorless by itself, but that is my opinion.