I've shot both ways, but now shoot 3 under. I'm much more accurate this way. While taking lessons with Rick Welch he told me that he tested extensively using both methods, and concluded that he was more accurate with 3 under. It won't be more accurate for everyone though. Do whichever feels better. I don't consider myself a gap shooter at all, but I know my brain subconsciously uses a gap. That gap is much smaller with 3 under, and it is easier for my little pea brain to compute!