My preference is 4 inch
I have S&W revolvers in 1-7/8 in, 2-1/2 in, 3 in, 4 in, 5 in, and 6-1/2 in, barrels. For general use I prefer the 3 in and 4 in barrels. For CC, the 1-7/8" works best, for hunting, I prefer the 6-1/2 or 5 inch barrels. If you're going for steel plates or paper...