If you give me the choice between a stubborn, grouchy big dog of unknown origin and a cute little white fluffy eager to please purebred that weighs less than 20 pounds, I'll take my chances with the grouch.
However: my old vet, the one with the overalls and the goats in the waiting room and the six rescued Greyhounds on her land, once told me this:
In a fight between any dog and a Chihuahua, she would bet on the Chihuahua, unless the other dog was a Greyhound.
Give it up for Paco, the crime-fighting, bad-ass good-boy of the day!