All of my dogs come from reputable breeders. I research extensively, go and visit where the dogs are, meet with the parents, get copies of all health testing/screening that had been done, etc.
All my dogs are part of the family and it is very important that they are well bred and I know the background they come from. Plus they are all trained to do other things. My lab is a hunting dog. My Australian shepherd our livestock, and my GSD is a trained protection dog.
Shelter dogs can be great for certain families but they can be a gamble temperament wise and health wise. You dont know their background, you dont know their genetics, and you dont know what they have experienced. That is just to much of a risk for me when I need the dog for a specific purpose.
I support my local shelter in other ways but I would not adopt a dog from them