theres carbon, alluminun, 2" and 4" vanes, different lengths, different grains,and different brands. how do i choose which one to use???

ill be shooting broad heads if that matters

It really doesnt matter what kind of vanes, arrows, grains, brand etc. as long and the arrow is correctly spined for your setup. And to find that out, either go to a pro shop and they will set you up or list your set up on here and someone can probably help.