This can be debated....like everything else in life, but I think "generally", most think the -4 was the best of the bunch (save those stupid Hogue grips). The -4 was the last year for forged hammer-and-trigger and was drilled/tapped for scope mounts. It had the new yoke retention system and the original cylinder stop stud as well. Some folks prefer the older frame design and the -5 introduced the new frame. The floating firing pin also came with the -5.