I have Joby, which for a sling strap, I think I like the best, but my wife got me a Cotten rig for my birthday. It will carry two cameras, but I only use it for one. I am hooked on It. I carry my D700 with the 70-200 and it is great. Nothing bouncing around. It locks in place and a 90 degree turn and it unlocks.
I use a cane to walk and this rig is the only thing I can use and in a pinch, I could carry my bag or two cameras as well. All the weight pulls down evenly on my shoulders. I am also a big guy and all the slings rest on my neck more than my shoulder. I have one of their G3 rigs, but they are introducing a smaller version called the Skout soon.
I was not sure if I would like it. But when I can get out it is all I use and it comes with a small tether so when it is not locked in it is still attached to the rig.
https://www.cottoncarrier.com/