I don't think the registry matters so much as the "quality" of the dog. APRI is one of the better newer registries IMHO. They have dog shows, put on seminars and do not register just any dog. APR on the other hand will let you register mixed "designer" breeds as long as both the parents are registered purebreds. You can do a search and read up on most of the different registries out there and what the requirements are. APRI also has a forum where you can learn from others much like you can here.
AKC and UKC are probably the oldest registries but I have seen a lot of dogs that are AKC registered that most definitely dont meet the standard. Also before they started requiring DNA testing there were a lot of puppies registered AKC that weren't even purebred although I am sure the purchaser of the puppies thought they were because they had AKC papers.
If you want to show your dog in an AKC dog show to work toward getting an AKC champion title then don't buy unless it is AKC registered. Otherwise, just make sure the pup you purchase is healthy with good temperament and don't worry about the "papers." JMHO
One more thing - as far as you shouldn't pay as much for a dog that is not AKC? - again IMO - I would rather pay for a good dog that I will be happy to share my home with for years to come then to pay for a sheet of paper with its name on it.
