I like the 3 points alot. My only gripe with this particular setup, is that if you tighten the front strap too much, it has a tendency to slightly collapse the forend. I guess that is actually a gripe with the not-so-rigid synthetic M1A stock, and not the sling.
You probably wont have the same issue with the wood stock.
I use the three points as intended, and find them much more versatile and comfortable than the 2 points. Especially with the weight of the M1A.
Never really caught on to the single point thing either. I hate the idea of something as unforgiving as my rifle, banging off my junk and knee caps...
Even on an AR, I prefer the three point.