Feathers all the way. Even over the "broadhead" vanes like quick spins and blazers.

Feathers are far more stable in flight.. accuracy
they retain their full shape while in flight where as vanes tend to flap around in flight... accuracy
they provide much better arrow control than a vane does because of all the little ridges that grab the air... accuracy
they are lighter and faster,
they are far more durable than vanes,
they straighten out a badly shot arrow far better and faster than vanes do... accuracy
they are far more forgiving - should they hit an obstical or your rest they do not disrupt the arrows flight nearly as bad... accuracy
feathers are virtually uneffected by extreme hot and cold temperatures where as plastic isn't... accuracy
they look soooooo much better than a plastic vane and isn't shis what we strive for while in the woods???????

The downsides are they cost more and you need to water proof them if you hunt in wet weather.