Conclusions :
"All these systems are excellent. All of them have The Mirrorless Advantage over DSLRs.
Sony has been the established leader with a 5-year head start. Technically Sony is a generation ahead of Nikon or Canon, but when you actually shoot with these cameras you immediately realize that the Canon or Nikon are what you really want.
Sonys have always had an obtuse menu interface that requires us to look everywhere to find anything. Sony's bodies are uncomfortable to hold for any length of time due to iffy or absent industrial design. We don't love the handling or menus of our Sonys, but we love the way they shoot once we get them set up the way we want them.
Nikon and Canon are a joy to hold and shoot, and their menu systems are the clear and well laid out ones we already know. Likewise, Nikon and Canon retain their superb color rendition, while the Sonys give merely OK colors, at least if you're as picky as I am (color rendition is always a personal artistic preference). Color accuracy, a technical measurement, is unrelated to color quality or color rendition, which are artistic qualities.
We all have our preferences, and this guide may guide you, For instance, I don't like that Canon is missing an auto brightness control on its finder, but the fact that all my EF lenses work flawlessly, it's the only model on which the shutter closes when you turn it off, it has a superior touch screen AF selector during EVF shooting and the EOS-R has a clever new Fv mode makes up for that. The Nikon's shutter stays open, collecting dust like Sony when it's off and it has only mediocre compatibility with old lenses, but it has a superior finder and one more control dial than the Canon. If you're starting from nothing, I find Nikon and Canon equally attractive overall, unless you have a real need for one or another area in which one excels. I wouldn't buy into Sony today unless you need the A9 for sports for this fall season or prefer two cards over good handling. We're all different; if you are OK with Sony's handing and color rendition then Sony is a generation ahead technically.
The final answer is that you should get whichever brand you already love; they are all surprisingly wonderful. Nikon and Canon's brand-new mirrorless are amazingly excellent. If you're invested in either Canon or Nikon, their new mirrorless work the same as your DSLR - just better - and give the same colors you love. If you're already in Sony and if you love the menu system and in-hand-feel, then stick with them."
