Originally Posted by
Urthdigger
This is true. However, it's a matter of efficiency. Cure II and Stoneskin have the same cost and Cure II is faster. If you're decently geared, Cure II will heal more than Stoneskin will protect, which is functionally the same (Both allow the tank to survive X more damage).
Cure II is basically better than Stoneskin, functionally, in every way except for one: Stoneskin can help the tank even if his HP is full. That is why I say never cast it on the tank unless a cure would overheal.