The six-foot staff is the most flexible in terms of range, since you can use it short or long, which you can't do with four- or seven-foot staves.
But my sigung, who was known (once-upon-a-time-in-Hong-Kong) for his staff technique (think about mob enforcers), favored the 5-6 foot staff and the lau gar staff technique, with its "yin-yang" grip.
So, since I don't go around beating people with sticks (whether for debts or honor or any other reason), I don't have a personal opinion about staff forms. But it worked for him...
