On the range comparisons of just these four revolvers - keeping in mind that we are talking just for use ON THE RANGE. In my opinion, that means for fun and skill building, or even to replicate for defensive use in the home or place of business. In other words, not for carry, concealed or otherwise.
I've owned 3 of the 4 of these in .357 Magnum, and the fourth one (GP-100) I have in a different caliber. I've shot a number of GP's in .357 Magnum, however.
I find the 686 to be the best of the four if all else is equal. It's got the size and durability, but I would swap out the OEM factory grips. If it's an old 686 with the big Magna grips, they look okay but don't feel great and they transfer far too much recoil energy. If it's a newer 686 with the Hogue monogrip, it feels pretty good but couldn't be any uglier if you pooped it out on a Friday night.
The GP-100 is a ridiculously close second place. I won't be convinced that it's any more "durable" than a 686, but I really doubt that it's any less durable. Typically, it'll cost you a little less money. The trigger is pretty darn good for what is generally considered a "lesser" gun. The older ones have a fine looking grip that feels pretty good, too. Newer ones have a horrific Hogue monogrip that just turns my stomach. NOW-- if the 686 in question is a newer revolver with the internal lock -AND- it's a 7-shot "plus" model, then I will move the GP-100 in to first place and never look back. This is a lot of gun and will last a lifetime. If I'm buying used (95% of the time I am...), I'm looking for a pre-lock 686. If I'm buying new, GP-100.
S&W Model 60 is a well-built little fireplug. But it's small. For range days, it's too small to be comfortable. It offers much more recoil than I expect from a .38 or .357 revolver, even when using .38 ammo. Mine had a great little grip that "felt" fine in the hand, but a different grip may have handled the recoil better. Mine was a three-inch, full-lug barrel and it was VERY accurate and well built, but the recoil made me sell it. I look back on it fondly -- but I don't miss it. Would have been a perfect carry gun if I were to carry a revolver. I do not.
SP-101, .357 Magnum. Much like the Model 60, for a few less dollars and a little less refined. The double-action trigger wasn't nearly as smooth and predictable. Build quality was solid, I would trust one of these without question, but I'd never buy one as a range toy or a practice gun. It's a quality carry gun, but a GP-100 is a much better choice for regular shooting.
All four are fine guns and any one of them would be a great one to own for different reasons. These four aren't far apart when it comes to utility, durability, build quality and value for the money.
Attention Brass rats and other reloaders: I really need .327 Federal Magnum brass, no lot size too small. Tell me what caliber you need and I'll see what I have to swap. PM me and we'll discuss.