FOr what you are talking about, the 586 or 686 for sure, I've had one of each, loved 'em, the 586 is definitely prettier, but for some reason the mechanism of the 686 was much smoother, and it was the barrel length I preferred, 4".
I believe it was the Registered Magnum that evolved into the M27.Smith & Wesson Distinguished Combat Magnum, later to become the M27.
The S&W models 19 and 66 are essentially the same gun, and an absolute pleasure to shoot
What is pre-lock?
There's A LOT of heated debate on the subject