Well pound for pound I would have to say a patterdale terrier. They use them to hunt badgers in the states{not honey badgers}. I have personally seen a 14 pound patterdale get out of his pen and jump a 50 pound pit bull and got both front legs torn completely off. The little f#cker was still trying to kick with his back legs trying to get back to the bulldog; all the while screaming and wagging its tail, lol. Dog died right there from blood loss; nothing we could do. I've seen video of them being held by their legs and dropped down into a badger hole and they for the most part won't come up without the badger, live or die.