Sorry for the resurrection of the topic but from my experience: 1) If you want to be any good, you should always be going for headshots. Even if you miss, you are still training to snap and track towards the primary target zone, and thus improving your aiming skill. If you ever need to switch to a 1-2 shot kill game like COD or BF, you will easily be able to adjust your now fine-tuned aim to go for center mass instead. But it's much harder to go the other way - training to just hit center mass, and then hoping you can get headshots later when it is critical. 2) The only exceptions are in general game situational purposes: i) The opponent is almost dead, and therefore bodyshots will ensure kill and reduce chances of missing completely with a headshot. ii) Your shot is bad (or bad at that time), and therefore you aim for more upper body/neck (not center mass). iii) You are sniping (either as covert, or just long range fire). Even when sniping, aiming for headshots are preferred, but there will be times on long range maps like beach, where you would prefer to just dole out damage to slow them down or keep them back. Conclusions:
Since aim drifts high and low over playing time, it is generally my feeling that as you feel more confident, you raise your crosshair higher up the body (even aiming to their hair or just above their head). This ensures more and more headshots, and better quality training on your aim. As you start missing shots, you lower and lower until you hit the neck, then stop. This allows you to not completely miss your shots, while regaining confidence and good aiming practice. If you gain confidence before reaching the neck, you can just start going back up again without ever reaching for the neck level.
That being said, even against AET or Euro players, I still prefer to aim above the neck, or even high. I feel that you can jump start your aim much better by simply aiming head all the way. Perhaps if I'm in an important match/scrim, I might play it a bit safer and aim lower for a few critical minutes where I know I can still get the kill with "body" ie. neck shots, but generally you will lose worse if you rely on that kind of aim against top players. Maintaining an air of confidence is really important.
