I have and use all of them. I shoot mostly weddings and children, but also little bit of "everything". Because you have had 85/1.2L II and have 70-200/2.8L IS II I try to focus on differences and how those lenses compares to 135/2L.
135L is lighter than two other lenses. It focuses fast, (almost) as fast as 70-200/2.8L IS II. I like the build quality and shape of that lens very much (not a tank, like 85/1.2). If you compare 135/2L to 70-200/2.8L IS II @ 135mm, there are differences. Since I take photos of people, I need more f2 than f2.8 with IS. 135 has better bokeh and less DOF to add some background separation. If I take full body portraits of couples AND I need both background separation and shallow DOF, I usually shoot with 135/2L @ 2.
70-200/2.8L IS II has nice versatility and overall quality. It's is always safe solution, but when you want extreme quality over versatility you want 85 or 135. Bokeh of those lenses is so nice!
Besides those lenses I also have 35/1.4L 50/1.4 and 24-70/2.8L. I use all of my lenses but, of course, I have my favorites. I love 35/1.4L and 135/2L. Nice size, superb image quality, fast focus. 70-200/2.8L IS II is also a great lens and lacks nothing. I do not enjoy using 85/1.2L as much as because of size and slower focus, but it is still one of my most important lenses and I still like to use it (a lot).