Either one is a fine choice. It just boils down to personal preference. You will get a hair better muzzle velocity out of the 3" barrel, but not enough that you would notice. Some say the 7 shot cylinder is a little stronger due to how the cylinder stops are between the bores instead of lined up with them on the 6 shot cylinder. Don't know about this there are a lot of standard 686's in the field and functioning just fine.