To me, the fundamental difference between MJ and WW is that MJ loves children (no smart remarks, but he really does seem to enjoy their company), whereas WW doesn't seem to get along with them very well at all, or particularly enjoy their company (or any other person's company, really).

Much as I really do like GW, I have to say I much preferred JD in the role. To me, GW will always be Young Frankenstein, and the gentle prisoner in "Stir Crazy" more than he will ever be WW. JD will be several characters simultaneously, because each one is not only different in personality but in appearance.