My wife has experimented with top and bottom round to make a steak she could grill, the sirloin or football muscle is too tough generally. She has had grilling loin down but loins are also the main ingredient in many of her Asian and Italian recipes so loins are always in short supply. Gilling round steak for us starts when we are cutting. In the past most of our steak has gone in to Swiss steak which we cut about a 1/2" thick. For grilling we have gone to cutting 11/2" to 2", similar to what a lot of steak houses do with a sirloin. Being thicker allows you to get some char without over cooking the interior. My wife starts with a marinade, anything you generally like but be sure it has quite a bit of olive oil. She starts with the grill pretty hot and reapplies olive oil when she turns the steak. Cook to an internal temperature of 135 and cover with foil and rest for several minutes before cutting. I love sautéed mushrooms on my steak while my wife could take them or leave them.