I've had good experience with the Cusco 1.5way, plenty of 'feel' from it where it counts. If you want something that feels a bit less aggressive the factory optional diff is still a good upgrade though.
Despite the hype I didn't rate the Quaife over the 1000+ miles I drove one, could give you a scare very handy but that's maybe more to do with my driving style. Unfortunately I haven't driven a TRD or Kaaz in enough anger to give an opinion.