They are in this order:
IV (you probably shouldn't do this, potentially dangerous and probably more intense than you'd want)
IM (very fun, requires needles though)
Plugging (surprisingly potent)
Sublingual (tasty stuff, makes your mouth numb and is a short head above snorting)
Snorting (still pretty potent, not too hard on the nose unless you're doing alot)
Oral (hit or miss, it seems)