686 no dash, 1980, introduced model
686-1, 1986, radius stud package, floating hand
686-2, 1987, changed hammer nose, bushing and associated parts
686-3, 1988, new yoke retention system
686-4, 1993, change rear sight leaf, drill and tap frame, change extractor, Hogue grips, the -4 eliminated the square grip frame on 4" and longer models.
The 686-4 is generally regarded as the apex of the design as the -5 introduced MIM parts and the -6 and -7 contain the lawyer lock.
The 686-4 is the top of the line, pre-lock 357 magnum. It does and will carry a premium price tag.
Now if you find a pre-lock S&W 686-4, 4 inch barrel with 7 shot cylinder... now you're talking the best there is. good luck.
Here are 3 of my 6 S&W 586's and 686's, all 686 7 shot S&W's, I love them: