Personally I don't care nor see why we need to compare Halo 3 with a game coming out in December. Why does it have to be Brawl, why not Galaxy etc. Is brawl the only game that stands a "chance". Personally I don't think so.
Also, both games are good for what they do to both company's. They are both going to sell well no doubt, they get the job done there we go. I do not see the big deal.