I have a 4" 686-4, and a 2.5" 686-6 plus. Both are excellent. I'm not a fan of internal locks, but I also don't really have an problem with MIM parts. I don't notice an appreciable difference in quality between the two.
It's obvious from most of the posts here that folks are biased, and so far, the only definitive answer to which 686 is the best, has been shown to be the one you have in your hand........
The 3 inch and 4 inch CS1 686's done up for the US Customs service are the most accurate and durable of the 686 series. They had to be to meet the contract specifications.
These days they appear to be the most desired and expensive of the 686's as well. If the Gunbroker sold prices are any indication. Regards 18DAI
I only have this 686 that I bought over 34 years ago and I can't compare to newer models but I love it over my python. Have used it on hog hunts and management hunts taking does out to 60 yds.
Post# 11 by Mr. Borland wraps it up pretty well. I have a 686-2 that I bought new and the stainless front sight with the red insert is detrimental to accuracy on a 6" revolver. I put FGC grips on it and besides the front sight, it is a nice and solid gun.