Carbon arrows are more durable which is cheaper in the long run.They also seem to be more tolerant to changes in tip weight etc.Most carbon arrows are able to cover spine requirements with a smaller number of shafts as compared to aluminum.This means you can change your poundage or tip weight (within reason) and not have to buy new arrows.Just make sure you buy quality arrows.Some of the cheaper carbons are not that straight and can vary in weight per dozen.As far as penetration it's all relative to the KE of your setup.I've never had a problem with penetration.

CB

WHACKEM N STACKEM