Neither, use the PerkStreet debit card. :D
Seriously, though, ask yourself this: Do you currently carry any credit card debt? If you do, the answer is cash.
Otherwise, you can do what I do and use a rewards credit card. The requirement is that you must pay it in full each month (most banks even allow you to automatically pay it off on each due date.)
The cash back is why I prefer credit cards, though some people will appreciate the boost to their credit score by responsibly managing credit.