Handgun or shotgun is what I’m leaning towards in dealing with such a threat. I wouldn’t say no to a good combat knife either. Dogs are tough, having wrestled them often working as a kennel worker for my first job.
The bad news is that they are very fast and won’t leave you much time to react, plus their jaws (depending on breed) can break bones and ruin your tissues in a hurry. They also can’t be rendered unconscious very easily. It would take a professional boxer or a ball bat.
The good news is that unless the dog is exceptionally powerful, an average size full grown man can overpower them in many cases. We are not the prey they were built for, and this leaves us a fighting chance. With a weapon, a person has a pretty solid chance even if they’ve already locked onto you. Without one? Fight as viciously as you possibly can. Rip his ears off. Poke at his eyes. If you have the presence of mind, reach for his legs and trip him down, and then get on top and attack ruthlessly. Also, dogs are difficult to choke, depending on breed, but it is possible. Don’t count that out, especially if you happen to have cord or string in hand.
If there is more than one… well, that’s serious trouble.