I have a 4" 686+. I voted for square butt because, for its weight, it feels right in my hand. Its frame allows either square or round butt, but came with a square butt grip that hooked up with a "stirrup" at the bottom of the grip frame into which the grip holding screw, um, screwed. That was a good grip. When I switched over to a Crimson Trace laser grip, that "stirrup" prevented me from installing it until I got inspired and yanked it out. The CT grip is just as good, indeed maybe a little better as a grip than the original, and it lights my fire. (Couldn't resist that!)
Cordially, Jack