I have all 3 of the mentioned lenses, and that's a tough choice (Since they are all my favorite lenses pretty much).
85L - Amazing bokeh, not much better out there for portriats, AF is a bit slow as you've been told, but hey at least it has AF (which the ZE 100 doesn't.)
ZE 100 - I love this thing, it is absolutely insanely sharp and has excellent contrast/micro contrast, the focus ring is smooth as butter, hard stops at Infinity and Macro, but I have to say I am biased towards this one since I shoot video and don't need AF. It does have focus confirmation, so the point lights up and it beeps when you have the focus right, and it's much easier to shoot manual focus with Zeiss lenses since the throw is much longer than on Canon lenses. I had the 100L before this and loved that one as well, it's 1/2 the price and you get IS and AF (although the AF is pretty darn slow on the 100L). If you need AF I'd go with the 100L, it's much cheaper. If you want the best, go with the Zeiss.
135L - I don't think anyone has anything bad to say about this one, it's one of Canon's sharpest lenses and the AF is super fast. It is a bit long to not have IS, but that's never been an issue for me. It's the cheapest of the bunch by a long shot.
I'd consider maybe picking up the 135L and then getting an 85mm f/1.8 to see how you like the 85mm focal length. For $300 the 85 1.8 is an amazing lens. Or if you can only get one maybe the 100L, it's a tough choice, but that's the most versatile of the bunch and fits all the needs you mentioned.
Hope this helps.