from what Anton once posted, magnets are the most resource intensive.  apparently, the number of children something has makes it more resource intensive. his example: a 100 segment snake would load easily while a 100 legged insect would take an age.  magnets have 3 parts and give a body part multiple children.  he posted about this to explain why V4 was so resource intensive.  given this, morphs are probably the lightest, and even bones used judiciously would better than lots of magnets.   personally, i'd be fine with correction morphs that were just named logically, so i could dial the correction for the pose.  but i'm not afraid of spending time with dials.