I've seen people hang, shoot themselves, jump out of buildings, lay in the railways and worst of all stab themselves. I watched the videos to see the true process behind these kind of actions.
I've come to the conclusion that the only way to get the best outcome is to prepare yourself, no matter which method you choose. Those who impulsively have chosen to CTB suffered from lots of pain because they were not ready for it. Except if it's instant death, it doesn't really matter.
It's just as painful to die as it is to live. Peaceful it is afterwards which won't matter as you'd be unaware of it anyway and won't be able to witness your success.