This is the way I like to do things.
Strength: Volgin was able to punch holes in the hull of the Shagohod, which RPGs couldn't blemish.
Speed: Boss, although not by much.
Striking: Volgin, his punches are very powerful and have good speed as do the occasional kick.
Grappling: Boss certainly exibits more skill with grappling, though Volgin's massive strength would give him some advantage in this department. Also when we see him beating Snake we see some grapples that involve punching too, though Boss has more skill and has a better advantage in this department.
Equipment: Boss has a powerful gun which fires rapid shots with unlimited ammo and a knife, Volgin has bullets that he ignites with his electricity and fires them with his hands, he can also use weak electricity so that he can control multiple bullets and then fire them all by surging them with more electricity.
Brutality: Volgin, he makes Ocelot look like a carebear in terms of cruelty and brutality.
Versatility: Volgin has a constant charge of 10,000,000 volts in his body, fires bullets with his hands, and stuff. He has much more ways to win than Boss.