It seems that 3/11 is more common in the DAN! circles. I theorize this is because they use higher doses and less frequent doses. This in my experience causes more sfx and greater need for time off. Also it means parents don't have to do it every weekend for their kids.
In the Cutler groups 3 on and 4 off is typically used in the early months. Many who can then tolerate longer rounds are encouraged to do so but there are details that should be considered. These are in Cutler's writings and in the Files of the Frequent Dose Chelation group.