Son are you gonna stirr up a hornets nest with that question,
There are many pro's and cons to both, Plastic is quieter in flight but less forgiving on the recovery, Feathers need to be treated regularly for water proofing, When Plastic gets a lil wrinkled it makes your flight a lil funky.
Now all that being said...You are shooting a cross bow so most likely the noise factor nor the forgiveness will be a problem..The rails on the crossbow do tend to be a little harsh on feathers so I personally would go with the plastic