https://www.dpreview.com/reviews/image-comparisonThis tool helps you view output from all the cameras. Sony isn't known to have good color, not sure why people thinks it does well at portraits.
Sony may do mirrorless well, but I haven't heard of many pros using mirrorless. I'm sure it happens, I even knew one. I don't see a digital viewfinder as an upgrade, just a couple years ago it was a serious downgrade to have a digital viewfinder.
Out of your choices, I'd go D850. Mirrorless is the new frontier that has everyone excited, and it's bringing in a rush of new sales. I don't think it's exceeded normal DSLRs yet.
If I really wanted a mirrorless Camera, I'd look into Fugifilm's new (cropped sensor not a
true medium format) medium format cameras or Hasselblad's DX1 II. But if I wanted a budget friendly option between Sony and Nikon, I'd pick Nikon. The ring is much bigger on the Nikon, and I suspect Sony has some vignetting in the corners of some lens. I read somewhere that Sony designed the mirrorless lens around a crop sensor ASP-C (like buying a DX lens in Nikon). Nikon overbuilt their lens mount and the size competes with medium format capable lens, leading to speculation Nikon has positioned themselves to leap into medium format.
Overall though, Sony is the leader in mirrorless tech. For a mirrorless camera, Sony has less lag in the viewfinder and the focus is faster. Mirrorless still sucks here compared to the older D850 if you're going to take picture of a kid playing soccer, a running dog, a flying bird, or anything that moves fast.
If you really want Sony, you won't be disappointed, even if Nikon Z7II significantly improved the shortfalls of the first Z7. Sony is still supposed to be the better camera right now.