Apparantly, after the stage where you really badly need to breathe, drowning isnt so bad. I wouldnt know though as I havent gone to that extreme, maybe someday though.

Getting burned, eaten, dismembered, decapitated or disemboweled are pretty bad ways to go.

Dying in your sleep seems like the best way, but I'd like to be conscience when I go. Leaving your body for good is an experience I'd like to feel.