Guillotines. Bow and arrow.
Guillotines are a speedy way to kill a stickman, but there is no long term pain. I once heard about a man who was sentenced to death by a guillotine and he agreed to blink his eyes as many times as he could after they chopped his head off. He blinked somewhere between 13 and 19 times, but I don't exactly remember.
Shot by arrows causes a lot more pain unless you hit the stickman in the head the first time.