Depends on your intentions. If you want to go to the airlines ASAP you can't do that without a CPL/IR so do that first. Then do the instructor rating as you can get applications out while you do that. I would say it is good to do the instructor rating though, for two reasons; the outlook for airline recruitment is not great at this very moment and you can build hours while you wait, and it will make it easier to become a training captain in the long run - or at least instructional experience will.