Frames, options, caliber and finishes.
For example the 66 and 19 are the same gun; the 66 is stainless and the 19 is blue. They are K frames, and two of the most popular Police Duty Guns ever. The 686 was the new (Circa 1983) frame that was heavier than the K, but still lighter than the N frame. The 686 and the 586 took the place of the 66 and 19 as duty weapons.
A 681 is basically a 686 except with fixed sights. Owning and collecting Smith & Wesson’s is a great hobby. There are catalogs written on all the models they have made over 150 years.
I picked the 686 for the best because the OP said “All aroundâ€. To me that would mean Duty, Carry, and Competition. While I love my J frames they aren’t Duty or competition weapons.