I am a registered nurse and I have taken care of burn patients, aids patients, alzheimer's....you name it. Many of them have died. In my personal experience, I would say that the very most painful death that I have witnessed would have to be death by cirrhosis of the liver. Every patient I have taken care of with this condition has had a very painful, slow, and agonizing death. Although I would say that burning would be a close second, I would choose to burn to death in a split second to avoid this outcome.