Shelter dogs are always best, as you are rescuing instead of feeding money to people that breed for the sole purpose. But, I wont go there because you are genuine in asking for help and information and probably unaware of the alot of what is out there regarding the breed.
If however you do buy from a breeder, make sure you see PROOF of the parents health cert and OFA. This breed can have and pass on several medical problems and the last thing you want to end up with is a puppy that you fall in love with developing hip dysplasia or a brain tumor.
A very touchy breed, be careful.Dont get me wrong, wonderful breed, but you HAVE GOT to be prepared.