Full disclosure, I have not used either. I have both the EF 85/1.4L IS and the EF 100/2.8L Macro IS. Generally, I'd take an 85/2 over a 100/2.8 for portraits, but my main portrait lens is the RF 70-200/2.8 (which replaced my EF 70-200/2.8 II). I may switch my EF 85/1.4 for the RF 85/1.2 at some point. I don't plan to get the RF 100L Macro, primarily because of the focus shift issue with the lens.
Besides the individual characteristics of each lens and macro capabilities, for portraits when engaging with your subject close up an 85 will typically be used for 3/4 to 1/2 body shots and a 100-135 for heads. YMMV based upon distance to model and use of strobes vs natural light. Like Neuro said the RF 70-200 (even the f/4L) will be a more versatile choice. The RF 100L will focus faster than the STM for one thing if you have more movement in the poses and that plus the superior optics will out it ahead in my book.