Muzzle down, right shoulder. Rifle balances better and stays in a more vertical position. Easy to control the muzzle with a hand on the fore end, easy to lift the muzzle up towards horizontal if negotiating uneven ground, etc. Easy to take the rifle off the shoulder one handed and under control without spinning it in a 270 degree arc behind me as I've seen some folk do when carrying muzzle up. For a long walk or very rough ground, dragging out, etc. I can lift the sling over my head so the rifle sits tight across my back and points at the ground a couple of feet to my right. It might not work as well if your rifle has a long barrel or very long moderator, but for me at 5ft 10 I find there's plenty of room to walk normally without fear of poking it into the mud.