[Anaru]

running AP means your "big" source of damage would be your shield & your Q.
granted the AP ratios are pretty ridiculous - but then you realize shield & Q are not spammable spells.

on the other hand sion's R gives him lifesteal which would be beneficial with stacked AD and attackspeed. i feel that the money invested in for AP doesn't pay off as much as it should.. and because sion's E requires HP, building attack damage & tanky, i feel, is more beneficial...

also the debate's not ad sion or ap sion VS other champs, it's just is ad sion or ap sion better (in general)

maybe it's just me.. i just never see ap sion work properly because he lacks proper cc besides his q & sustain without lifesteal & ad