Burnese Mountain dogs are excellent dogs, not overly bred and not commercialized.
if bred properly, there shouldn't be any genetic health problems eventhough hips are the concern.
they are actually good guard dogs as well as good family pets. Not much of a hunting dog, they were not bred for it, but they are multi talented.
get one that smells good, well cared for pups should not have a bad smell.
Choose one that suits your own personality. personally i like the ones that resist you and fight you all the way. but if you are easy going, don't get one that tries to wrestle you hand away from you.
health wise, get one that owns the ground, one that walks with one leg slower than the other is out, one that drags the stomach is out. if you can hear the breathing, out.
clear eyes, clear a$$ hole, strong tail.
I trained police K9 for over 30 years.