This is kind of like asking "what's the best bow" in that you will get lots of opinions and they are all just that. I've tried shield cut from 4 to 5.5 inches and parabolic from 4 to 5 inches. I've tried both three and four fletch. What I've noticed is that they all work pretty well if your setup is well tuned.
So I've finally settled on 3 x 5" shield cut in either white or bright yellow. They don't really fly any better than any of the others, but I can SEE them the best. The older I get the more difference that seems to make. I've been shooting white lately because I have lots of them, but I'll be going back to yellow next time I buy feathers because, as I said, I see them a bit better than the white ones. I suppose the ideal would be bright yellow flu-flus, but I'm not quite ready for that much drag...yet.
And, yes, this is my opinion, so take from it what you will.