Most interesting purebred dog Ive ever met was a Dutch Shepherd. Beautiful dog, he was police trained, and very protective of his handler. You had to watch how close you got talking to the trainer, or the dog would really try to eat you up one side and down the other.
Most interesting cross, Id have to say my childhood dog. A Siberian Husky and a Cocker Spaniel cross, the result of my sisters dogs tangling. They were both indoor dogs, so there was no way it was any other dog in the mix. They were all beautiful, and I wonder what happened to his littermates. We had to put mine down due to severe child aggression problems. Bit several times. It was really heartwrenching to go through.