The more helix, or twist that is on the fletching the more stability imparted to the arrow in flight. The helical configuration causes the shaft to rotate during flight which gives the shaft stability during flight. This becomes especially important when broadheads are used, the broadhead wants to steer the arrow from the front and the fletching needs to counteract this from the back. As far as rotation and stability the helical will impart the most, offset less and a straight fletch the least. The type of rest will also dictate what you can use.