A thumbs down from me...
I’m a Sony A7R II user who moved from Nikon but kept all my Nikon lenses, and also have a few Leica M lenses for when I want a tiny camera-lens combo that’ll fit in a (large) pocket. I bought the Sony as stopgap, intending to upgrade to a newer mirrorless in a year or two. The major reasons I went from an SLR to mirrorless are, in order of priority,
• I prefer a good electronic viewfinder over an optical one (you capture exactly what you see)
• IBIS (my manual lenses obviously don’t have image stabilisation)
• I’m no longer tied to a camera brand, and can use almost any lens regardless of age or maker
• lighter and smaller.
I’m not wedded to Sony (really Minolta) - I use mostly manual lenses with an adapter, which means I’m now not tied to any camera brand. I have no intention of buying a Sony autofocus lens. So, I feel I can view all three mirrorless cameras somewhat objectively (granted from my preferences).
The Sony does its job but has no soul and its menus and massive number of options are ... irritating. So, I’ve been looking forward to the Canon R and Nikon Z.
Neither the Canon nor Nikon excite me. The Sony A7R III has far better features, and is more versatile. The Canon, in particular, is unappealing with its lack of image stabilisation. I suspect image quality will also be below par - Sony/Nikon sensors have far superior dynamic range, something I often need. Compared with the current Sony A7R III, the Canon and Nikon seem almost a generation behind.
Also, neither has dual card slots - my Sony A7R II doesn’t either, which is one reason it’s a stopgap: this lack is a problem for photographers (like me) who cannot afford to lose images (I’ve had a card die - albeit just one).
Finally, Sony made its e mount specifications public. Nikon has refused to do this for its new mount - as will Canon, I suspect. This will make manufacture of third-party adapters more difficult, possibly affecting performance. Clearly they’d like to lock me into their systems and for me to buy new Canon or Nikon autofocus lenses: no thanks.
In short, the Canon R and Nikon Z seem to be marketed users of their SLRs to stop them moving to Sony. Unlike the Sony A series, which are aimed at all photographers regardless of the brand they use.
So, no thanks Canon (I’ll give it 4/10) or Nikon (6/10). I’ll stick with Sony (8/10) despite its irritating ergonomics and menus - unless the former shape up and confront Sony head on.