I prefer the look of just doing it with the head. I especially like the speed from it. When you use your whole body to duck it is slower and it makes tricks like gatm harder. I want to focus on getting it in the right position when I kick it up, closer to my body so I won't be ducking behind it at all. I was actually trying to do a double gatm, which was what got me in this bad habit. Never really came close to it though 
Although I've never trained GATM, I can do Reverse GATM (ATM Ducking NT) pretty well and clean with the technique I described. Thing is, if you do it only with your head, it's really easy to do it unclean since you don't have that feeling of ducking under the ball, IMHO.