For most desireable 686 I'd vote for the scarce CS1 variants. Particularly the 3 inch tube versions. They are allegedly the "best made" of the 686's due to having to meet government contract specifications in durability and accuracy.
Overall the most desireable 686 "dash" appears to be the 686-4. All the best engineering changes without any of the cost cutting/cheapening of the model that came later.
The 686 I like best is my 4 inch 686-4+ 7-shot. Very nice revolver with a great trigger. Regards 18DAI
S&W Model 19 Combat Magnum. Everything you need in a revolver, and nothing you don't.