hanging can be painless and "quick" too if you compress right spot you will fall in unconsciousness and die in next minutes... problem is to do it right. You can endup in pain and die "slow" or even survive. But same can happen for train,jumping or firearm, I saw videos how people survived from train or firearm and it was horror like scene. If we think about it, with good rope and anchor point, hanging is more reliable than anything else, there is still risk that you will die in pain and it wont be quick.