I know very little about breeding dogs, but I know a bit about genetics and a bit about evolution, and basically the more different two within species animals are the better for the survival of the offspring. The more similar and closer related the more unhealthy the offspring will be.
If I was buying a puppy, then I would look for a pup that had some pedigree background, was kc reg' had all the health checks, and whose pedigree's were not overloaded with champions.