I'm pretty sure it was Mas Ayoob, in his class in August, who told me "Nobody ever looks at a Doberman or Rottweiler, and says 'you don't have the ****s to bite me.' "
One more advantage to the large dog... A burglar may try to bluff a home-owner. A burglar will rarely try to bluff a dog.
Note to mods: Not trying to get around the language filter, per se, but it's a direct quote.