The sharpness and color rendition of the 135mm is, in my opinion, even better than the 85mm--but, as our "studio space" is so confined, the 135mm is an outdoor and larger venue lens for us. Since the 135mm focuses so extremely fast and has such a wide aperture, it is a great combination of super-flattering portrait lens and action stopper.
But for working intimately with subjects for a portrait that reflects mood and character, and for which the subject is posing, the 85mm somehow brings a contemporary and timeless feel that cannot be surpassed. The ability to go to a truly workable 1.2, and when at minimum focus distance get just the plane of a single eye perfectly in focus, while all else dissolves into a dreamy softness, was just too much for this photographer to resist.
I believe that you can't go wrong with either, provided you find the scenarios better suited to each.