Depends, If there's something you want to buy at EB with your store credit in the near future, keep the store credit there using your credit card to purchase DJ Hero. Then again...by using the store credit you'll have a credit card free of debt / money in your hand.
If were me? I'd use the store credit, that way you have usable money for other items If needed, rather than in store credit that can only be spent on games.
My opinion.
MyPS3 Miscellaneous
3 days / Sydney Northen Beaches, The Watcher