Mixed! At least, I've only ever had a couple of purebred dogs, and many many mixed. The biggest thing for me is the individual animal rather than its breed, as well as the animal's needs. If the animal is sitting in a shelter needing an understanding human to give it a loving home, it's always going to have priority to me over the cute little puppy that was purposefully bred to make the owner money or even to continue the better qualities of a breed. Whether the animal that needs me is a mixed breed or purebred makes no difference to me, only whether we have personalities that will get along well together.