Go with a 4", much better holster options and the perfect amount of gun in a .357. You will never need a second handgun, unless your contract the illness.
Great advice for carry and HD and range. 4" Best overall, but they make the 686 in more barrel lengths than any other product they make, so pick the one you prefer. The 686+ is my choice, I like the seven shots. If you are savvy and frequent shows and stores, and are patient, you'll turn up one just like you want. I prefer the ones with no locks and frame mounted firing pins with either case hardened lockwork or stainless lockwork. MIM is okay, mine is MIM and is phenomenal, but I like my revolvers like swiss clocks.
You can get a new one and have a fine revolver too. You can disable the lock if you like, I did mine and the way I did it you can't tell anything was done, the lock still looks fine it just doesn't work. Besides being ugly, and a sign of defeat to the antis, the lock can and has, albeit rarely, seized up and engaged due to inertia. It isn't supposed to, but I've read stuff about guys that had this very probelm. Mostly in the scandium ultralights, which is capable of unseating the other rounds, heavily crimped, in the cylinder due to inertia --this will lock up the revolver too. This has happened to me personally. Just beware.
And if you get the illness, sorry, no known cure. Best off just getting the one you like best and going from there, trying to rationalize the purchases based on carry needs and range needs and so on and so on...