We don't call them shepherds here we call them sheep station owners. unless you are talking about the Australian blue cattle dog. they are quite smart however they can get a little temperamental, so you have to watch them if you are not the owner. Australian Shepherds are pretty much like any other dog, whether purebred or cross. Domestic dogs have been bred over centuries to work for, and be companions to, humans, and in the vast majority of breeds unpleasant or unwanted characteristics have been bred out.
All dogs can be aggressive, but in the very few instances where individual aggression is actively encouraged for whatever reason - guard dog work, for example - this needs training from puppyhood to bring out the trait as a main characteristic. It's a very bad idea to train or keep dogs for the purpose of making them aggressive.
Different classes of dogs, particularly working dogs such as the Aussie Shepherd, show different characteristics: herding, hunting, pointing, retrieving, speed, burrowing, swimming, ratting, rabbiting and so on. Highly nose-driven breeds are trained as sniffer dogs; other breeds are trained as companion dogs.
The intelligence of any breed, or any cross, is usually extremely good. Dogs can retain quite a high vocabulary, particularly if the humans around them talk to them a lot (preferably in proper language, rather than in puppy baby-talk: it doesn't matter to the dog, but can make you look silly in public when the puppy's grown), and dogs can be trained in many ways.
People will say such things as 'cattle dogs (or other working dogs) need a big yard and lots of exercise, or they'll be destructive,' or 'this breed will bark all the time if left alone,' but - like intelligence - the way a dog behaves is as much about its upbringing as about genetics; it is, after all, as a domestic animal destined to live all its life in an artificial environment.
A puppy left to cry alone in its new, strange home without its mum will very possibly grow up to bark when alone, and may even become nervous or fearful. Reassurance and cuddling for a week or so will reward you later with a dog that is happy being alone.
Any dog accustomed to exercise only once a day will settle into that routine. Working dogs on cattle stations (farms) can spend some time out working and the rest of the time in an enclosure: their life isn't necessarily all about spending hours and hours charging around after sheep.
My own dogs are Gordon Setters, which are a gun dog breed. Bred to run with the guns from dawn to dusk, they'll happily settle for resting when their owner rests and chasing a ball from time to time.
So when you're choosing a dog, think more about size than breed facts and myths. Can you afford to feed a huge hound?
When it comes to characteristics of different breeds, try this: think of say, six, different breeds of dog. Then look up a homepage for each breed on the internet. You'll find every one described in words such as 'intelligent', 'loyal', 'affectionate', 'beautiful temperament', and so on. Just change the name of the breed and it all reads much the same!
Ask me and I'll tell you the best dogs in the world are Gordon Setters...
Remember, the kind of dog you'll end up with depends on you; on the way you treat it from the start, and on the way you train it. Never be reluctant to take advice, and always be slow to follow that advice...if it doesn't sound sensible, ask someone else or use your own commonsense. And always be gentle; never shout or hit. There's no need, and no excuse....!!