Would it be better to get enough DEX to frequently be able to hit with light attacks, and have more ATP?
-or-
Would it be better to get enough DEX to frequently be able to hit with power attacks, and have less ATP?
ATA > ATP
Use light > hard > hard and you won't have this problem o_O
the second choice. the problem with the first is that if you can only hit with a light attack, then you can't really force an enemy back to stop them hitting you, and if you are a HU doing close combat then you're screwed! also, a power attack will do double (ish) that of a normal attack, and your talking about a LOT of atp to double your damage, but the ATA required to hit consistently over not isnt much.
also, what AS said, he got there a sec before me, but if your having problems wit that do a light before the enemy reaches you (if your meleeing, if not just do l,l,h) then do a light that will hit, then end with a heavy, oir just do 2 lights then a heavy. light heavy heavy is the most useful one, as the light will stop the enemy and so you should not have a moving target for your heavy attack.