I know this would most likely depend on which ship your flying, what upgrades it has and how it fits into your squadron, but generally speaking, if you could hmchoose an extra attack or an extra defense die, which would you choose?
Attack has better odds, and can remove an enemy before they can shoot you, but most ships/pilots only get to shoot once per round while...
Defense dice can be used more than once per round of you are attacked more than once and keep you in the fight longer so you can do more damage.
I would have to say is rather have an extra defense die.