Why AP Galio over tank Galio? So I've been playing Galio before he was popular(hipster glasses) and he's been one of my top picks. I usually run him solo top with flash/teleport and I play him mostly as a tank. However nowadays I've seen many people say AP Galio is the way, building Rabadon's, etc. 

Why is it? I see that Galio is one of the most effective tanks, and he gains quite enough AP through his passive to be effective. Building Chalice of harmony, Merc treads, Aegis, etc. give enough burst on Galio to kill caster minions immediately with the Q/E combo, even when leveling W first. 

So, what makes AP Galio superior to Tank Galio?