They don't make it in the size category but might be good in other areas:
<---breed website for the PWD
But I would go with the happy black shelter mutt too! Also agree on the Doberman as a no, even with the houndy ears.
I think a regular Lab, from a super duper smart breeder who looks at health intelligently could be good. Flat Coats are a big cancer breed from what I understand.
I always look at what the breed was bred to do - is this a dog that was meant to work with people, and in what capacity.
No way I would want a Mastiff or any type of large protection breed that doesn't necessarily look to their person for guidance. I like Chows, but there is a reason all that nasty is in a small body.
The Boerboel is a large, mastiff dog breed from South Africa, bred for the purpose of guarding the homestead. These dogs were often a first line of defense against predators and were valuable in tracking and holding down wounded game.
Another probably too small:
The Bearded Collie, or Beardie, is a herding breed of dog once used primarily by Scottish shepherds, but now mostly a popular family companion. Bearded Collies have an average weight of 40–60 pounds. Wikipedia
: 14 to 15 years
: Active, Intelligent, Alert, Lively, Hardy, Self-Confident
: Fawn, Black, Blue, Brown, Tri-color, Black & Brown
: Female: 20–21 inches (51–53 cm), Male: 21–22 inches (53–56 cm)
: Female: 39.7–59.5 lbs (18–27 kg), Male: 39.7–59.5 lbs (18–27 kg)
The Landseer is a dog breed. Many kennel clubs consider the Landseer to be simply a black-and-white variant of the Newfoundland, but the Fédération Cynologique Internationale recognizes it as a separate breed. Wikipedia
: Black & White
: Playful, Intelligent, Courageous, Generous, Patient, Loving
: Male: 28–31 inches (72–80 cm), Female: 26–28 inches (67–72 cm)
: Male: 130.1–149.9 lbs (59–68 kg), Female: 99.2–119 lbs (45–54 kg)