Working breeds tend to be the more intelligent of dogs; and for good reason. Humans way back in rural times bred these dogs to help with pest control, hunting, tracking, herding livestock, and guarding the homestead.
I do think mutts potentially make the best dogs. Especially if they inherit the best characteristics of its breeds. Both of the dogs I grew up with were part German Shepherd, and they were great dogs. Barked whenever a car they did not know pulled into the lane, and they kept the coyotes away.