I've heard that it's just preference what feather you use.
As long as you use the same for all your arrows, you should get "predictable" flight and consistent pattern. I find natural feathers will almost always try and be helical naturally. All my turkey feathers I fletched straight, but had to "force" them into it.
I think from now on with my goose feathers I will use helical.
I dye them different colors for left vs right (red=commie=right
). I also organized them in brown paper bags. (left primary, left secondary, right primary, right secondary etc.)
Never mix them. (unless you want to sabotage someone)