I own both. They are very different lenses with very different uses.
For controlled portrait sessions, the 85L is where its at. Shot at the wider apertures, the 85L creates a sense of dimension that could never be replicated on the 70-200. Granted, the 70-200 can nuke the background to a blur of color in a way the 85L never could if that's your thing. I prefer to keep the background elements in tact, as it gives a portrait context.
The larger apertures on the 85L allows you to keep the background elements in the frame, while blurring them out and isolating the subject enough that the background does not become distracting....creates a beautiful sense of dimension and pop.
The 70-200 is more of an event lens for me. Great lens optically, but its most useful for me because of its flexibility.