I conceal carry almost daily. I also shoot Defensive Pistol Matches with my revolvers every month. The 2 revolvers that I turn in the best times with are my 3" 66-2, and my 4" 64-2.
Of these two I conceal carry the 3 Inch 66-2 in a Lobo Enhanced Pancake with Optional Inner Hammer Shield quite a bit more than the 4" 64.
The 3" K or L Frame would be my pick for an all round carry gun. With a 3" most Models of S&W revolvers have a Full Length Ejector Rod. The 2 Inch and 2.5 Inch ones come with short rods. You get more positive ejection with the full length ejector rod.
Also a 3" Barrel is about as long as is handy to conceal carry year round for me. The 3" K is a little more compact, however I am sure I could manage a 3" 686 just fine. I do not own a 3" 686 for a simple reason. The new ones are all 686 Plus 7 shot models. Shooting matches using my carry guns is very important for me. I use Safariland Comp III speed loaders to load my K and L Frame 6 shooters. When you go to a 7 shooters you are back to the HKS Speed loaders which are not nearly as fast to reload with.
No I do not conceal carry the Comp III speed loaders. I do like to use them to beat up on the Combat Tupperware at the matches however.