I'd cut off his leg because if I had to lose one it is the one that I would chose. My reasoning is that I use my legs for standing and propulsion only, where as I use my arms for holding, manipulation, moving, etc. My leg would be easier to replace and in an average day I touch more with my hands than I do with my feet, so I would lose out on a lot more (touchscreens, holding hands, using remotes, etc)