Sony is growing by leaps and bounds, but one of the biggest advantages Canon and Nikon continue to hold is the deep investment a lot of their users have made in native lenses. This great video examines the current state of affairs for adapters and if they can work for you.
Coming to you from The Camera Store TV, this helpful video will show you just what you can expect from trying to use adapted lenses on mirrorless cameras in 2018. I'm personally shooting mostly with a Sony a7R III these days, and I've found that that in combination with a Metabones V adapter actually works better for my Canon 85mm f/1.2L II lens than a native body, as the adapter still works about as quickly as a Canon body, but there are no AFMA errors as one encounters with DSLR bodies (even after years of AFMA adjustments, this lens is still finicky for me). Combine that with Eye AF and my keeper rate went up substantially when I switched to a Sony body, so much so that I now trust the Sony enough to make it my main body for a lot of work. If you're curious about their system but married to a lot of Canon or Nikon glass, now is a good time to watch the video above.