The Op-Tech strap has been my main strap for years but I also use the Black-Rapid when carrying a bigger lens like the 200-500. The main thing I find awkward about the Black-Rapid is changing lenses. With the Op-Tech, it is very quick and easy because the camera is held at a good height and twisting one lens off, switching the rear cap and twisting the new one on seems very fluid. I have yet to find a as smooth a "rhythm" with the Black-Rapid.
My balance is not what it used to be, and I do a lot of mountain trails with dicy footing. For that reason I've given up on straps and carry my camera in a ThinkTank sling bag (Model 20 V.2.0). I can swing it around and get the camera out in a jiffy. And if I take a spill the camera is well protected.
I used Optech for a while a few years ago and then tried Black Rapid, but seldom use straps now.