These two supps don't fall in the same category, so I would say stack em. I've done them both at the same time and I enjoyed it.
If you're looking for increases in natural test, strength gains, vascularity, and aggression (which is probably what you're looking for) then get JW. If you're looking for natural increases in GH, better sleep, and a better sense of well being then get PowerFull.
Otherwise I don't think you can compare the two.