Cyanide may involve more pain/discomfort (by most accounts, it does), but its a lot faster and more certain than SN. I chose SN but only because its easily accessible for me, if I had a choice I'd take the cyanide because I really want to die, 100% all the way down to the bottom. Don't quote me because I'm not completely positive, but I think I remember reading that cyanide was totally reliable for death at the proper dose and there's no antidote (as opposed to SN, which can be easily and quickly counteracted by methylene blue)