CoG/iCoG or 9th Anniversary Prime?

Even if you're going off the bare minimum of what you posted (15), it still comes down to 1 att vs 6 all stat, which is roughly where most people end up at.
I would just go with the attack unless you're a Xenon. The all stat is going to be a lot less siginificant at end-game once you've got a decent amount of % Att built up, plus if you scroll all of your equips with the Prime Scrolls you'll be severely lacking in attack anyway.

i dunno if i have bad luck or what, but my luck with chaos never takes me over 10 attack.