I typically use flank or skirt. Inside is more common but outside when I can get it. I don't marinate. I make a wet rub consisting of EVOO, for the liquid (not to soak in just to lubricate it), unsweetened cocoa powder, cumin, chili powder, Mexican (if I can get it) oregano, some salt, and well chopped fresh garlic. All that is whirred together in my little Cuisinart food processor. I rub that on the steak and then let it sit a bit while heating the grill. I use higher heat on the inside skirt, lower on outside or flank