I don't think you would be very disappointed with any of the options. For video and stills, the 85L & 35L are gorgeous on the 5D MkII, but I tend to shoot them around f/4 as the subject can go out of focus by breathing when either of these lenses are shot wide open on video.
As far as the Canon / Sigma debate, part of it comes with how deep are your pockets and do you do this for a living? I happen to have a Sigma 50 1.4 (older finish, for what that's worth) that is sharp wide open and handles quite well. It gives a slightly different look that the Canon 1.4 or 1.2 and has a slightly wider field of view.
Chris brought up a good point though, you may want to wait for the new 24-70L II. I have heard through good sources that it is as sharp as the 70-200 2.8 IS II, which would keep you from having to switch lenses on a shoot (and keep dust out on location).
Last, but not least, erwinrm brought up a very good point on the Rokinon lenses. You can pick up several different focal lengths very inexpensively, and when shooting video, you are in manual focus mode anyway.
Good luck with your search!