OK, so I've said this often - and that is that I'm a multi-brand camera slut. Thus I shoot with the EOS M, Fuji X, Micro 43, and the defunct (yet still very competent) Samsung NX line of cameras.
Having said all that, cameras from all of those brands are capable of generating superb IQ results and oftentimes it's difficult to choose which one brand to settle on. What then comes into play are differences - some tangible and some intangible (often difficult to put into words). So where to begin?
Alright, these are my opinions and yes, they are subjective because no two folks will use their cameras in the same way. I'm primarily a "stills" shooter and have not gotten my feet wet with video (although I know that sometime in the near future I'll belatedly embrace that process), so my remarks are based on stills shooting only.
1.
Micro 4/3 - I've been with the Four Thirds system since its very inception back in 2004 or so with the introduction of the venerable 5 MP Olympus E-1 (which I still occasional use by the way). Then transitioning to M43 became a smooth scenario and I was glad to see that the IQ levels were as good or better than the previous regular Four Thirds system. So I cannot fault M43 cameras in any way. I've owned a bunch of those cameras and right now I'm using the E-M5 (original Mk I), E-M10 Mk II, E-P5 Pen, and the Pen F and I've come to appreciate their ergonomics, and capabilities. I particularly enjoy using the Olympus versions of M43 cameras mainly due to a preferred (warmer) color tonality, and IMO, a bit more DR than what I managed to get with my Panasonic cameras when I used them. In addition, I found that Olympus cameras generate far better skin tones than their Panasonic counterparts, although from what I've heard and read, that is gradually changing in the Panasonic line as newer models are being released.
Recommendation -
As I always tell folks, "do NOT discard a particular camera (or system) in hopes of jumping to another system. If you can swing it, by all means pick another camera brand, purchase one of their cameras and then do your evaluations (without parting with your previous cameras).
Fuji X system - I took a chance (experimented out of curiosity) and purchased the Fuji X-E1 and kit 18-55 F2.8-4 IS lens 6-7 years ago. At the time of that Fuji purchase, I was shooting Canon, Nikon, and Micro 43 cameras. From the moment the X-E1 arrived, I became hooked on Fuji's way of doing things, camera design, and their generous and loyal "Kaizen" system of FW updates. Currently I'm using the X-T2, X-T20, X-E3, X-E2s, X-H1, X-A5, and X-T100.
What I've come to enjoy with Fuji are:
1. Camera designs (both rangefinder and DSLR models) that sport superb ergonomics (again, subjective I know).
2. Exceptional Dynamic Range capabilities. Among all of the mirrorless brands you are considering (from your OP), you will find that the DR capabilities of the Fuji system far exceed what you may have been exposed to with the M43 line of cameras. In addition, I am able to pull far greater dynamic range (in particular with RAW files) with my Fuji cameras as compared to the other brands..
3. Exceptional high ISO (read "clean" here). Whenever I have to shoot in very low light and need clean high ISO images, I instinctively reach for my Fuji cameras. I now shoot regularly at ISO 6400 through 12,800 with no issues.
4. Two types of sensor design: 1) First obviously is their X-Trans sensor design, and... 2) they have an entry level and intermediate Bayer sensor line in their X-AX series and X-TXXX series. Both cameras generate a superb color tonality with rich, dynamic colors.
5. Excellent skin tones - self explanatory here.
6. A large system of lenses - the largest of any APS-C camera system. Even the entry level basic X-C line of lenses product superb IQ capabilities.
Canon EOS M system - to put if simply, a "fun" system to use. Canon produced a system of mirrorless cameras that keep in line with what mirrorless camera designers originally had intended - that is, a far smaller system of models that are light, convenient, and have exceptional IQ. As an aside, if you look at many of the Micro 43 models being released now-a-days, they are getting as large as regular DSLR's - not so with the Canon EOS M line of cameras. I'm currently using the original M and M2 (because of the colors), M50, M100, and M6.
The one area of the EOS M system that I've had an issue with for a long, long time, is the lack of dedicated EF-M lenses - of which there are not many. Sure, you can use the adapter and use a variety of larger, heavier EF-S and EF lenses - but IMO, that then defeats the purpose of having a smaller camera system. Others may not mind. And if you are primarily a prime lens shooter, than there are 3rd party versions available for the E-FM system. However, if you use zooms (like I do), you are limited with regards to very good, very sharp lenses in the EF-M system - other than the wonderful 11-22.
Samsung NX - I won't go into this system (although I enjoy using it very much) because it is no longer available.
So in the end, as I mentioned - all cameras are capable of generating superb results. What will differ are how colors are rendered, dynamic range capabilities, high ISO results (again, read "clean" here), menu layouts, and ergonomic considerations.
Right now, the one system that I've been focused on for a good 50-70% of the time is the Fuji system for the reasons I delineated above. Am I saying that because somehow I dislike the other brands? Hell no, as I enjoy using them all! But I have to be forthright here in that if I were forced to discard all of my camera brands except one, honestly...I would keep and maintain the Fujifilm cameras and they do have a loyal following (and the numbers of new users are growing). But the likes of the X-Pro 3 represent a dilemma. You will either like this camera, or you will hate it. It's certainly not for me. But it would be your cup of tea - just keep in mind the other variables I mentioned above with regards to Fuji cameras.
Good luck...