I use a harness that I made myself. It supports the camera hands-free on my belly and doesn't allow it to swing around and bump stuff, but it's in the ready position like a neck strap would be, and I can grab it one-handed and swing it up to take a shot almost instantly. The harness also distributes weight equally to both shoulders, so I can wear it all day without much fatigue.
I like the concept of sling straps, but I don't like how the camera hangs with them - at your waist, upside-down, swinging and twisting around so that you have to keep your hand on it almost constantly to prevent impact damage. The big advantage is that since your hand is on the camera constantly, you can swing it up to take a shot quickly.