This is thread is about self-defense against dog attacks and given the subforum topic, it is about strategies and tactics to use in dog attacks and how to train to use those strategies and tactics effectively.
With this in mind...
Canines have certain instinctive traits, some breeds of which these traits are stronger while others are less so.
Also just as important is breed capabilities.
There are breeds of canine far more aggressive than "pit bulls" (a slang term, by the way, not a breed). However, many of those aggressive breeds are far less capable of causing serious injury compared to others.
Those annoying little Chihuahua's, for example, are very aggressive dogs. But few people give those little pipsqueaks serious thought when it comes to actual physical danger.
A German Shepard, however, is taken quite seriously, even though they aren't as stupidly aggressive as the Chihuahua.
And don't even touch wolf-hybrid canines. (That's another discussion.)
It's often what the breed can potentially DO that actually worries people rather than their actual aggressive traits.
All that said...you can find a dozen lists online about aggressive dogs and how they're ranked...and likely find they're all ranked differently even if they contain several of the same breeds.
What this really means is that people's first line of defense in an actual canine encounter is understanding those instinctive traits and how to apply that knowledge.
- Canines are territorial. In general, if you remain outside their actual territory they are less likely to actually attack UNLESS provoked. Actually violate their territory and attack may be unavoidable.
- Physical acts/behavior on your part may trigger violent/predator results in the canine. If you ACT like prey, then you will be PERCEIVED as prey. If you act like a dominant predator in your own right, then you MAY stave off an attack. This doesn't mean challenging the canine on specifics, like territory or food, for example. If you place the canine in a position where it feels like it must act or lose what it perceives to be its own, then attack may be unavoidable. If you exhibit stalking behavior, a canine WILL pick up on that and warn (posture, growling/barking) and/or attack.
While sudden violent animal attacks out of the blue aren't something you can necessarily ward off by leaving/changing your behavior, encounters in which the danger is advertised by the animal first can often be successfully avoided if you understand their behavior and work to mitigate the danger and leave.
Actually killing the animal should be a last resort for a variety of reasons. If you pre-emptively kill the animal, then you took no action to mitigate/avoid the encounter which may mean it was needless. If you force an encounter, you'll likely find out how quick/agile those critters can be and how difficult it is to actually physically defend yourself, with or without deadly force. Killing the critter is of little solice if you have to go the rest of your life with scars and other physical injuries to show for it. And I'm just talking about the encounter itself, here. There are legal issues, problems with neighbors to consider, and any number of other issues that probably ought to be avoided entirely.