Both are capable of producing excellent macro shots (if you define "macro" as no more than 0.5X magnification). Your expected use(s) should probably determine which one to pick. Both have comparable IS and both are exceptionally sharp.
I own the RF 85 f/2 and it's becoming one of my favorite lenses. like all longer lenses, it has less perspective distortion than a wide(r) angle lens because of the "flattening effect" of the greater working distance. The focal plane is, of course thinner at any given aperture, but for most macro shots these days focus stacking is used instead of small apertures, so that can actually be an advantage for the sharpest images.
The longer working distance also makes subject lighting much easier in most situations. I also own an EF 35mm f/2 macro which I've used on both EOS R and EOS R5 with adapter. For my applications, which are typically 3-dimensional objects like jewlery, insects and flowers, I use the 85 f/2 90% of the time. The available working distance makes it much easier to light subjects and the RF 85 f/2 is also a superb portrait lens. The 85 mm's IS on a R5 is amazing and hand held shots at 1/5 sec with a still subject are usually sharp. Alternately, the 35 is also useful as a nice landscape lens.
Since both are great at other uses beyond shooting macros, I'd suggest that you consider your other possible applications in your decision process.
