For a carry gun the standard 4" rules. The mountain gun version is not enough lighter to notice a difference on the hip and the slight loss of weight in the barrel results in a slight gain in recoil/muzzle flip. I currently own a 629-4 mountain gun and a 629-3 standard 4".
I shot no better and did not notice any increase in shooting comfort/recoil reduction between my 629-4 6" and 629-3 4" non lugged versions so the 6" went away.
For a range shooter or hunting version the 6.5" Classic with its full lug really tames the recoil/muzzle flip,its probably the best for a shooter. I own two 6.5" 629 Classic DX versions.
No flies on the 8 3/8" classic as a dedicated hunting revolver but its a little too much for anything else. I own a 629 Classic DX version.
The most versatile and best all around IMO is the 5" classic in either 29 or 629 form. I own a 29-6 5" Classic, a 629-3 5" classic and a 629-3 5" Classic DX.
