Okay, I have to chime in on this one, being the dog lover of course.
I have to start off by saying that people stereotype all breeds too heavily and dogs need to be judged individually as there are nasty tempered golden retrievers, wimpy german shepherds, labs that hate water and many other examples of dogs that fail to live up to their stereotypes.
Pit bulls I have rescued more than any other breed and mixed pits and I do have to agree they are a dog best chosen carefully and raised from puppyhood, although there are many good adult pit bulls in rescue if you know how to pick. But they can be a very healthy, strong and tough breed and is by far the smartest breed IMHO if you wanted to choose a dog breed on survivability alone, they would be number one on my list.
The german shepherd is an extremely versatile breed used for many purposes around the globe and also a very smart dog. Where your pit bull would probably not herd and might not guard, this dog would. They don't tend to be as healthy however.
If you ask a lot of hunters they really like their brittanys and german shorthairs if you asked for "versatile", and I have to give a nod to my personal favorite dogs, rhodesian ridgeback, the only dog considered to be a sight and scent hound and resistent to parasites and an excellent guard dog, but all three of these breeds are higher strung and aren't known to be particularly healthy. And brittanys are probably a little small for pulling a cart.
Two dog breeds I cannot help but mention simply because they contain so many individual dogs that are really really good dogs are the labrador and the golden retriever. But they are prone to a lot of health issues these days too.
And border collies are one of the smartest breeds and can be taught to do many things, and they are excellent herders which might come in handy as well as being strong enough to pull.
There are many mastiff-type breeds that would be useful for the pulling aspect and guarding aspect, many breeds fall into that group and deserve mention.
Personally, one dog would not be enough if TSHTF so you might want to have a pittie, a shep, and a couple of retrievers to go with your ridgeback, if you asked me, and personally, I'd pick a border collie too.
But then, I'm savingdogs......