Best transmission fluid brand highest quality for 2014 E250 W212

Recommended by manufacturer works assuming you change it once in a while. Other than that hard pressed to not get into best oil type discussion which usually doesn't go anywhere meaningful. Some have used amsoil with success apparently, I just went with the standard replacement fluid. Original stuff lasted 100k miles although I wouldn't recommend that. I just don't think it was ever changed in my car before I bought it with higher miles. Generally be it oil/trans/diff/xfer case fluids its about getting something that meets the specs and more importantly changing on a regular basis.