painful: buried alive then slowly suffocating or sliced up and slowly bleeding to death

painless: besides in your sleep.... hmm.... shot in the back or the neck

I'd have to say the most painful way to die I can think of is being stabbed and cut slowly till you die.
The most painless is probably a shot to the head.
It's over as soon as you fire that gun. .__.
I don't think you'll actually feel anything because it's just so quick.

I think being stabbed,burned, or tortured to death would be a very painful way to die. They seem like a slow process to me, that feels like forever to get over with.

As for least painful, I guess dying in your sleep would be it.

Most would think a fiery death would be the worst, but in reality Drowning is the most painful. Suffocating is the worst way to go.

Now, this may seem weird but Jumping off the empire state building would be the most painless. When you fall at that distance and speed your body naturally goes unconcious. You wouldnt feel a thing