Actually, it's not tricky at all since the question specifically asked about English quarterstaff, the term most people use to refer to a "short staff."
The perfect length depends on you. The Englishman George Silver directly addresses your question in his 1599
Paradoxes of Defence:
"To know the perfect length of your short staff, or half pike, forest bill, partisan, or glaive, or such like weapons of vantage and perfect lengths, you shall stand upright, holding the staff upright close by your body, with your left hand, reaching with your right hand your staff as high as you can, and then allow to that length a space to set both your hands, when you come to fight, wherein you may conveniently strike, thrust, and ward, & that is the just length to be made according to your stature. And this note, that these lengths will commonly fall out to be eight or nine foot long, and will fit, although not just, the statures of all men without any hindrance at all unto them in their fight, because in any weapon wherein the hands may be removed, and at liberty, to make the weapon longer of shorter in fight at his pleasure, a foot of the staff being behind the backmost hand does no harm. And wherefore these weapons ought to be of the lengths aforesaid, and no shorter, these are the reasons: If they should be shorter, then the long staff, morris pike, and such like weapons over and above the perfect length, should have great advantage over them, because he may come boldly and safe without any guard or ward, to the place where he may thrust home, and at every thrust put him in danger of his life, then can the long staff, the morris pike, or any longer weapon lie nowhere within the compass of the true cross, to cross and uncross, whereby he may safely pass home to the place, where he may strike or thrust him that has the long weapon, in the head, face, or body at his pleasure."
