Lock prejudice won't result in a better choice of revolver. I can't comment comprehensively on S&W's production through all the decades, but based on my experience and everything I've learned, it's inconsistent. It didn't change with the beginning of the "lock era," but it changed several times over the course of S&W history and was not uniformly better or worse with the advent of the lock.
The craftsmanship and quality were almost certainly at their zenith during the C.R. Hellstrom era, but by the end of 1965 that golden age had begun its end. In my mind, there are few production guns that exude the quality and craftsmanship of a 1950's S&W, but fine examples of those guns from 60 or 70-odd years ago are prized by collectors and not always especially practical. Looking at the much more abundant and prolific 70's and 80's Smiths, the quality of these guns is more often lacking than not. I believe revolver production slowed in the 90's through the end of the pre-lock era. What I've noticed about current production S&W revolvers is very poor quality control, but excellent production standards and technology. They have the machines and tools to produce a fantastic revolver, but it seems they ship everything without looking at it. Fortunately, they support their products after the sale but it's a pity they've chosen to let their customers do all the QC.
The rifling on current production is ECM (electro-chemical machining). It's amazing if it's done right. I have one barrel that just stuns me when I examine it under high magnification. It's perfect. It may not result in any meaningful difference in how the gun shoots, but I've never seen rifling produced by any other method that is so exactly uniform on the surface. The gun looks better on the inside than on the outside.
Some people still complain about MIM (metal-injection-molding) parts, but these parts are more consistent than anything comparable that S&W produced in its prior history. The parts do not lack hardness or durability at all. I rate them as easily better than the old pre-MIM parts. What can be superior to a MIM part might be a wire-EDM part but those aren't always economical on full production scale. But the old parts machined from bar stock or a forging were not better. At best, they were as good as a MIM part. They had a far greater chance of being inconsistent due to a problem with the tooling or the operator during the machining process.
People can form their own opinions and make up their own mind about what they want, but the revolvers produced with MIM parts and ECM barrels are better in every way than the old ones. The lock has no practical effect on the gun and it's lame not to consider new S&W revolvers because they're better. They're not the same thing as a Hellstrom, Gold-box era gun. But a 70's or 80's or 90's gun isn't better than the ones produced today. There's a good chance they're worse. I suggest checking the quality of a new one before buying, expecting to send it to S&W to have issues fixed, and then enjoying the better technology of a new gun.
The 686 is better than the 586 or 19 too. That's more my opinion, but I believe the balance and shootability of the 686 are better with a 4 or 5" barrel. The 19 is still really a .38 Special that's been magnumized. They did a better job of magnumizing it on the 19-9 and 66-8 than they did on the earlier versions but it's still better suited to 38 Special or mid-range magnums -- not because of durability, but because of shootability. The stainless steel frame and round butt of the 686 is better than the 586. The blueing and square butt look good but the blueing causes me too much fuss and the square butt forces the use of an antiquated grip shape. The round butt can use all the round butt grips as well as conversion grips that give the shape of the square butt. Note that the 19-9 even though it is blued uses a round butt. I like grips that are slim or narrow and while the 19-9 "Classic" has slimmer grips than the traditional target grips, I'd rather take the rubber grips, toss them, and find some aftermarket grips I like best.