While we're on generalities of health, I'll tell you my opinion on pure breed vs mutt. Many times mutts do seem to be healthier, esp compared to breeds that have endured a popular phase. The popularity increases the likelihood that puppy mills will have the breed and reproduce without regard to health, relationship, or any responsibility on their part (contracts). As you increase the number of dogs breeding, you naturally increase the odds that a mutation will show up. If that mutation shows up with a disreputable breeder and they breed anyway, then they have just passed on the possibility of that mutation being established in the population of that breed. That can be multiplied if they breed dogs that are related and both have the mutation. So, that is one aspect of why it often seems that pure breeds are not as healthy. This has been a great selling point of people that purposefully breed mutts and call them 'designer dogs' under the guise that they are a hybrid with "hybrid vigor.' (BTW, they are not a hybrid or the offspring would not be able to reproduce. The added 'vigor' is the fact they have reduced the likelihood of both parents having the same mutations. Therefore the odds of something predictable showing up in that particular puppy are decreased BUT the odds of something unexpected have increased. The puppy can still carry the recessive traits of both/all breeds involved and pass it on to their offspring. I won't even get started on all the recognizable mixes (and purebreds) dumped every day. . . ). Examples of breeds with a lot of health problems are the breeds in the top 10 or 20, or breeds with a very 'unnatural' physical characteristic (think: dachshunds and bassets with the long back, or pugs with the flat face and bulging eyes).
Of coarse, if you pick a breed that is not well known (wheatens, cresteds ;-) ) then you have a breed with very few health problems. They are generally raised by people that care and won't continue breeding a dog that has problems. The benefit of a pure breed vs mutt is that you know pretty well what to expect long term from your little ball-of-fur-puppy, both in personality and health. With a mutt, it is anybody's guess. If a person is willing to stick it out, then fine, but I've always liked calculated risks better. With a wheaten they have basically only 2 health issues. Skin allergies and protein wasting. None of my dogs have ever displayed any indication of either and I certainly wouldn't breed one if it did. I would have it neutered and place it in a pet home. Personality wise, i can pretty much promise that you will always get a "Wheaten Greet'in" when you get home. I don't know why, but this breed is know for loving to jump up on you and give kisses. I don't personally care for the kisses (they have to settle for fingers) and we have to work around the jumping if I'm dressed up (which is so rare it makes the dogs bark anyway . . ha ha!) It is true that they stay very playful and puppy like all their life and really don't have the typical terrier personality. Mine even get along fine with the cats, even though they weren't raised together (however, my cats don't run from the dogs, so that may be why the dogs don't chase the cats).