I owned the 100f2. I liked it but it flared wildly when shooting sunset portraits, losing a ton of contrast and showing any dust that was on the front element in the flare. I didn't like it at all. With the 135L my angle of view is narrower so I can get away with pointing the camera a touch closer to being in line with the sun when I wanted to use the sun as a rim light.
I may be an odd man out on this one, but I actually like the 100mm FL for portraits. A lot of the times the 135L is too far away to be directing couples who are awkward in front of the camera. Having to walk back up to them repeatedly to tell them not to move out of the pose after every shutter click(they can see my flash fire, thinking they can stop holding each other) because we're going to be building on the pose to get different looks . If the location is noisy, the extra 2' closer helps, allowing me to not have to yell. In a perfect world I'd have the compression of a 200mm lens at the working distance of an 85mm lens.
I will most likely trade my 135L for a 70-200 f4IS(for headshots which I shoot at f8 and to have a 200mm in my bag) and buy a new 85mm, just not sure which brand.
Though the lens I regret selling the most is the 100L macro. I miss that lens a lot.