My first and best answer is still that it should've ended after II, with the drive into the unknown future.
Since that option has been stomped to death, I'll go with the infinite time loop, so that everything that has happened since the first frame of the first movie turns out to be totally irrelevant to how the battle will end in the future.
My third choice would be an altered future in which Skynet is programmed to save humanity, so it destroys all of the nukes and the major stockpiles of chemical and biological weapons. That then leads to the unexpected result of world warfare as the playing field between all nations becomes level and mankind returns to the timeless tradition of killing ourselves.
Since that option has been stomped to death, I'll go with the infinite time loop, so that everything that has happened since the first frame of the first movie turns out to be totally irrelevant to how the battle will end in the future.
My third choice would be an altered future in which Skynet is programmed to save humanity, so it destroys all of the nukes and the major stockpiles of chemical and biological weapons. That then leads to the unexpected result of world warfare as the playing field between all nations becomes level and mankind returns to the timeless tradition of killing ourselves.