Our dog is a pure bred. I think when we were first contemplating a pet we thought we might actually breed and raise dogs so that is why we wanted a pure bred. But, it turned out that we weren't able to breed him - it was one of the conditions. Well, I should say we could breed with him but we wouldn't be able to have papers that the puppies were from a pure bred line. I think that was a way for the breeder to keep the lines pure.
But, it didn't matter. We don't use him to breed - he is just our pet.
I don't know if I have a preference - but even growing up my parents raised and sold pure breds. Guess I'm kind of used to it.