Length of life or quality of life, I don't think these are parallel to each other all the time. I would prefer to quality, so as long as I am convinced to quality of my life, dying early should not be a problem because of my sleep too much or less.
Obviously that would be ideal, but it's easier to determine what is improving the quality of your life (since you have direct, immediate feedback) vs. what is improving the length of your life (where you won't find out for years and by then it will be too late).
