It's not something I ever want to do, but you never know.
I'm not sure how well typical euthanasia injections work on snakes. Maybe someone can shed some light on that? If it is one of the painless and less messy ways, that would most likely be my first choice.
I'm uncertain of the other methods though, and would rather get it over with quickly, with a method I know will kill them instantly. In this case, blunt force or pithing. As long as the brain is destroyed, they no longer feel anything. With everything I've heard about chopping the head off, I wouldn't, couldn't ever risk it. The very thought of the snake possibly still feeling everything is just...