I thought the OS one featured the same optics as the 70-200 II without OS.. Which means that the only difference would be OS.
Still, I think the 70-200 II seem to be well worth it's money compared to nikon/canon 70-200 2.8 lenses.
The os version is not much cheaper then canon/nikon ditos.
So imo, you should choose the one without OS.
But just one question, do you need the 2.8 aparture? If not, then canon has it's 70-200 f4, which is such a sharp and great lens. If I ever were to buy canon, I'd get that lens and the 400 5.6 in an instant!