That would be the Labrador.
Mutts because they can't be over bred and all defects are coused by over breeding but mutts with lab in it are the healthiest
Sorry but labradors can be prone to hip dysplasia. Generaly the healthiest dogs are those that have been bred for many generations for their ability to work well. Such as racing greyhounds. There are many such that have been retired from racing looking for good homes.