>>343560881
>foot: 
top of foot. the top of the foot lets you move your foot in such ways as extending, pulling back, rotating, etc, the foot, that ankle can't do at all.
ankles should only be used for dancing and other especially athletic activities where you think foot will slide around or fall off or something. 
(ankles also seem to make IKTweaks look a bit odd. if there's any advice on this i'd like it)

>hip:
front, back, and side all have strengths and weaknesses.
front is my usual go-to. it's reliable (for my base station setup) and out of the way. problems are sitting down with the knees up (blocks tracker) and it stops you lying down on the stomach.

side is nice, but i hate bumping my forearm against it.

back is most useful for certain lewd positions, and laying on the stomach. if you're corded, sometimes your cord will hit the tracker and be a little fidgety though.

another very good option for certain things is at the crest of the hip bone. excellent position for emphasizing hip motion. really lets you dance expressively.