Traditionally, skirt steak or flank steak is the choice for carne asada, but you can also venture into other cuts like hanger steak or even flat iron steak. Since the beef will be spending a few hours in the marinade, you don't want to use prime, expensive cuts of meat. That's why less expensive cuts are preferred.  Hanger steak: This is a beautiful choice for tacos because hanger steak is very tender and flavorful but it's not as lean as a tenderloin. This cut comes from the area under the rib and runs along the diaphragm. It usually had some nice marbling throughout that makes it tender and flavorful. One drawback is the membrane that runs along the muscle in the center, it can be a little tough to bite through.  Skirt steak: It’s a long flat steak that runs along the ribs of the cow, relatively lean and has intense beef flavor. It can be a little tough so it's preferred not to cook it to no more than medium internal temperature and slice thin against the grain.  Flank steak: It's also a long flat steak that is adjacent to the plate where skirt steak comes from but closer to the rear and it is very lean. This steak cut has even more beef flavor and is leaner than skirt steak. Don't cook it more than medium-rare and also slice it thin against the grain.