Most painless and easiest? Just put a big blanket over your head and suck on the barrel of a 12 gauge. Lesser shotgun rounds will probably still do the trick. Most rifles will do the trick, as will pistols, but the further you get away from a 12 gauge (vaporizing your brain) the more of a change there is for surviving with some sort of horrific injury. This will be instantaneous death if it works. However, I would encourage you to find some way of enjoying your remaining days alive. Whatever you're going through, you can probably pivot and create some sort of life for yourself.