I would want to wield a dog in a manner that would cause it to bite my attacker. I'm not entirely certain how that would work. If you have any ideas, I'd love to hear them.
I've owned standard poodles and Sealyham terriers. Those two are pretty high on my list of favourite breeds.
I also recently came across a picture of a Swedish vallhund and it's the weirdest looking thing. It's like if you crossed a corgi with a wolf. I don't think I've ever seen one in person though. Those Northern Inuit dogs they were using on the first season of Game of Thrones were pretty cool looking too.