I chose to get a purebred cavalier and not a shelter dog -- and assume many of us did -- for the same reasons the first family chose a particular breed -- they wanted the reliability of a given temperament, size and appearance (with the latter in this case, the fact that the breed often can cause less allergy problems though no dog is actually hypoallergenic despite what might be said).
Shelter dogs typically bring their own set of issues -- totally unknown temperament, often there are some behaviour problems, they tend to be very poorly assessed by pound, shelter or rescue workers (a big gripe with me) and if they are puppies, you have little idea of what type and size of dog you will end up with.
I needed a small indoor breed that was bred to have a tolerant temperament and would be good with my cats. I also liked the way cavaliers looked and many other aspects of the specific breed (and I don't like yappy smallies!). I have done plenty of rescue work with pound dogs over the past years and support many general rescues here, but never had much interest in a pound mix (setting aside one single dog but while he was in foster it was clear he was a manic cat chaser so that ended that). I know I could have worked to get such a dog from the pound, but I simply didn't want a pound dog. I wanted a cavalier and given their heart issues, I wanted a breeder known for longevity in the lines and good hearts (and both dogs of his breeding are over 5 and heart clear).
There are pros and cons to both pedigree and poundies, dogs from breeders and dogs from rescues. Even running a rescue (or rather precisely because of that!!) I would be the very first to acknowledge that a rescue dog, mixed or purebred, does not suit all homes and even when one does, it is usually on a dog by dog basis -- not all rescue cavaliers suit a given home either.
I prefer to support health focused, dedicated breeders in whatever breed.
I know others that absolutely love mixes and get their dogs from the pound or rescues. (My Lily by the way was a pound cavalier! And came with her own set of challenges all right! :lol
Irish vet and Daily Telegraph columnist Pete Wedderburn looks at the issue
here. He also looks at whether pedigree dogs are not as smart
here.