Board Thread:Game Discussion/@comment-11256055-20130718075252/@comment-11118722-20130718125520

It is important but the damage you take is lower in proportion to the square root of Defence not the Defence value itself so an increase of 1k in Attack is more valuable than 1k in Defence, according to the way Deck Power works.

Additionally, the extra Defence may give 1 extra hit but it's not 2 hits instead of 1, it's more like 8 hits instead of 7. If you can raise attack by 20% you can offset the 14% increase in no. of hits.

Finally, if (typically) your characters have little health left when they die then they would still die in the same number of hits even with slightly higher Health or Defence, but higher Attack would produce more damage.

I can't think of a way to theorycraft this further without some real data but gathering it would slow down play so much that most people would be at risk of missing their goal tier.