For more than 30 years of slinging arrows, I have tried them all. Feathers, vanes on straight, angled and helicaled and have had good success with all.
It depends on your set up. Straight vanes on a shaft that is well matched to the bow and head will work fine, but on a shaft that is on the edge of being to stiff or flexable will cause havoc! Thats when helical can make the difference, giving a little more drag on the back of the arrow.
I always seem to end up with 3, 5 inch helical vanes for both 3D shooting and for hunting though. (I shoot my hunting bow for 3D's)I also prefer a heavier shaft, like Carbon Express, Terminator Select 6075's, for added kenetic energy.
I have never been a "speed freak" so I dont mind slowing things down a bit.
For feild archery, I do shoot 3, 2 inch straight vanes on a light weight ACC and a small point for the speed. It gives me a little more up and down error range at the longer shots like 55 to 80 yards.