I'm going with amount.
Long hours at physical labor, (or some repetitive work) = back pain, other health probs, not great pay/bitterness feeling inside.
Long hours at brain labor, (creative, sales, etc.) = burned brain/empty well syndrome, disillusionment, loss of humaness, heart attacks
Shorter hours at physical labor = less health probs, happiness, or at least, more enjoyment of life
Shorter hours at brain labor, (creative, sales, etc) = better product/result, more human satisfaction/sense of accomplishment, less heart attacks
There's a reason CEOs go on lots of golf trips, and why even middle management emps get to go on perk trips where pleasures are inexpensive.