I have searched all around for "The Best" camera sling and finally found one with the Wandrd Sling Strap. It's very easy to attach and remove from the camera. The best part, it leaves nothing dangling when removed. The strap is comfortable and soft. I wore it for many hours with my camera and lens that weighs about 3.5 pounds with no problem. The sling is quick to adjust, which I like. I normally shoot though the view finder, but when light starts getting low, and I am not on a tripod, I'll shorten the straps, and push the camera out and use the back panel. The quick adjust works great for that.
If you're searching for a sling, definitely check this one out. It's not too big, nor too small, it comfortably carries my full frame mirrorless with monstrous lenses as well as my M4/3 with it's petite lenses.