Don't waste your time. I've used both and chose the 135L on the extra compression and the stop of light and that was on just my 5Dc's green tinged screen. If your arguing that the 100L is a better portrait lens, your mistaken. Many already agreed to the 135Ls clear superiority in portraiture and that's what the OP is going to do mostly.
I have used the 135 too, indeed I still own the FD version of it. I am not arguing the 100 is a better portrait lens, what I am saying is for the vast majority of users most of the time they couldn't tell the difference between images from either, that is a very different position to assert. Throw in the macro ability, full weather sealing and the hybrid IS and for most people the 100 makes a "better" (more useful) lens.
Consider this, there is nothing that the 100mm macro can do for portraiture that cannot be done on 70-200LII, while the 135L gives me twice the light of either for effect or practical purposes.
The 100L is a fine macro lens, and my original comment said that it can be used as a portrait lens. I prefer the 135L.