For those of you who are uber-potion masters of uberness, tell me...what are your potion strategies? Not in making potions, that's alchemy...but in buying them or using them to best effect?

Like for instance, is it worth it to buy the lower level health potions, or just buy the most expensive/powerful ones?

Do you even bother buying potions or just find them? (For those of you who do not do alchemy, that is.)

What are your most useful potions and what ones do you never bother with?