Boards
The way Steve Albini has his guitar is WAY better for your back
but can anyone get away with wearing it that way without looking like they're just trying to be Albini? Probably not. *sigh*
But yeah, wrapping your guitar strap once round your waist instead over over the shoulder puts all the weight on your hips. It also means you don't need to worry about your guitar headstock dropping suddenly and cracking the floor if you have to bend over to fiddle with your pedals.