As long as the bar is racked properly and you maintain proper body positioning, I don't think it makes much of a difference. I've used both.
For obvious reasons, Oly lifters are going to want to rack it in the way that replicates catching a clean. If you don't do weightlifting, though, I really don't think it matters.
Look at all the powerlifters who front squat. They're front squatting a lot more than most/all Oly lifters, with two front squatting over 800 lbs. None of them can do the full grip rack position, and there doesn't seem to be any issues with stability.
tl;dr - how you actually rack the bar across your shoulders and proper body positioning matter much more than how your hands are touching the barbell.