You're browsing the GameFAQs Message Boards as a guest. Sign Up for free (or Log In if you already have an account) to be able to post messages, change how messages are displayed, and view media in posts.
Critical Attack is easy to get so I usually use it until a more useful potential comes along. It is very useful for boss killing. Penetration is good for killing troops behind sandbags -- especially through sniping. I am not sure but Critical attack might work anytime at the start of your attack so it probably works against tanks and definitely against armored infantry troops.
Crit Atk is better against personels as this potential make all our shots deadlier as if we're shooting at enemy's weak spot, and the infantry's defence isn't always high anyway so we don't need to ignore defence in this case.
Tanks have way too much defence so even if we were targeting their weak point, those tanks hardly could be scratched so Penetration would def save the day.