Metagross and Tyranitar would go out as one of the firsts due to Garchomp's Ground type. Dragonite and Salamence would negate this and keep going. Sazandora might hang around long enough. It would eventually boil down to Dragonite, Garchomp, and Salamence, but Salamence's insane speed and attack stats could end it for a win. And it pains me to say that since Metagross is my fave psuedo legendary.
did you forgot that tyranitar will pwn garchomp with blizzard as it has 4x weakness exactly like dragonite and salamence? also hes immune(like sazandora) to psychic.
oh, and he is having sand stream, which boostes its defense by 50%. so ground moves will be only 1,5x effective against him.