I own an 85 1.8 and a 135 2.0. It's a really unfair comparison.
The 135 is an amazing lens, but the cost can be prohibitive, while the 85 1.8 is priced well and because it's not built to L specifications for the body (the glass itself is really quite good), is very affordable
Focal length, the 135 is a classic lens for full frame, while the 85 would be about the same focal length on an EF-S type camera.
The third stop is in favor of the 85, but the additional focal length favors the 135.
It's apples and oranges to me. I own both, and own an EF-S, 1 series, and full frame camera.
bottom line is that you get what you feel you need, and nothing else. If you regularly shoot sports that would require the shorter focal length or third stop, the 85 is a great choice. Longer focal length would favor the 135.
I owned a 135mm f/2L before, it's a sharp lens no doubt. But the 70-200mm f/2.8 IS gave me much more room to shoot under low light, I sold it and used the $ on a 1D body. I now own a 100mm f/2 specifically for portraits; I don't have any problem with CA; for value and performance, I think it can't be beat. It's a perfect match with my 1D
