Haven't had much of a chance to do anything photography related over the last couple of months, but I am currently shooting with a mirrorless camera when I do get the chance.
I bought a Sony a7R Mark II.
After using it for a while now, I would say the following:
1) Amazing sensor, the files are so malleable it's ridiculous, and with 42mp there's no worries regarding resolution.
2) While very limited in terms choices available - there are a handful of excellent small/light manual focus lenses either to suit directly or that can be adapted relatively easily.
And that's about it. If you're willing to treat it as a technical exercise at extracting the nth degree of image quality (from a sub-medium format digital capture device), it's absolutely amazing. So that's two positives.
1) The menu system. I actually cannot understand how they managed to get it so badly wrong. Settings are all jumbled up, not in any even vaguely coherant groups. Video settings are scattered in amongst still image settings, camera hardware settings, etc... Nor order, badly named, enough said.
2) The colours suck. They're really dull, and quite cool SOOC, and "feel" very different to edit to the Canon RAW files.
3) Custom function buttons don't understand the difference between AF and MF lenses. If you set a custom button a function to do with focus, ie: set AF focus point - it doesn't jump to the manual focus equivalent when changing to a manual focus lens. Having 3 or 4 custom function buttons sounds great in theory too, but in reality they just end up masking features that should have their own dedicated buttons/control wheels - ISO settings and focus points for example.
4) Ergonomics - Small is great in theory, but it is a bit too small for my hands. I would rather a full size D-SLR with less unnecessary features/weight.
5) Build/sealing. They feel like they would be quite susceptible to damage, and definitely don't give off that rugged and dependable feel of pretty much any Canon D-SLR 7D and up.
6) Resolution - Awesome in theory, but in reality almost no lenses are up to the task asked by a 42mp full-frame/35mm sensor. It magnifies many flaws that ~22mp sensors never even see, and anything but the sharpest lenses will look very mediocre due to diffraction when stopped down. Epic image quality when you find a lens that can deliver, but...
7) Lens availability. There's precious few lenses available, either native or adapted - and most of them are either rubbish, overpriced or both!
Expense - horrendously expensive, and given what a dog it is to use - it really doesn't deserve the premium.
It suits me, because what I want it for is more still life/landscape type stuff so I just work around the mountain of usability issues.
But I wouldn't want to use it in a professional environment, because it just doesn't feel dependable or consistent enough. And I think that about sums it up. The Canons might not be at the head of the pack in terms of sensor tech (fingers crossed the 5D IV will fix that!), but they are so versatile, consistent and dependable they can be a lot more practical overall.