It is all situational with distance, time, relative movement, barriers, and background all playing a role.
IIRC, Nyeti used to train folks at his old agency to go for a head shot at close range--I believe they had a fairly long string of successful OIS incidents ending quickly and decisively in favor of LE when using that tactic...
Take a look at the FAST test--two shots two a low percentage "head" target about the same size as the eye region and then four shots to a COM type target.