Ahem..
When different breeds mix. The genes of both parents go to the puppies. .. Those puppies could get EVERY genetic defect from every breed it is mixed with. And maybe only get the genetic defects from one of the breeds, Or 1 defect from each of the breeds.. etc etc.
Neither are better. But that "a mutt has less chance of getting genetic defects" is a load of bull.
Health wise, mutts have no back round, same goes for agression and temperment. Ussually with a mutt, you cant even tell which breeds are there. It could look like a half lab half German shepherd and guess what, there might be 20 other breeds in there. Genes are passed down from dog to dog. just because you have a black mixed breed mixed wit another black mixed breed, doesnt mean your not gonna get white puppies, red puppies, fawn puppies and brown puppies.. Right?
you could get a truly aggressive dog mate with a friendly dog and it has non aggresive pups with great temperments.
A female from that litter could have a litter of pups with great temperments.
A female from HER litter could have pups with great temperments.
But uh-oh. a female from her litter, mixed with another stable dog, could have a litter full of truly agrresive (not just reactive) dogs.
Niether is better. Things can happen with mutts so well as they can with purebreds.
IMO, getting a pure bred from a reputable breeder,stacks the deck in your favour.