I think it's awesome that you are going to a shelter to get a dog!
Australian Shepards are great dogs. I'd go with an older dog if I were you. You are young and puppies are a ton of work. They go to the bathroom inside,chew up everything, etc. The thing about the shelter is that the people working there don't always know if the dog is housetrained,etc. That's because people just drop their dogs off there or they are abandoned dogs. Shelters will let you come in and walk through and see all the dogs. When you see one that you like they will let you take them out and walk them,pet them,play with them so you can see if it would be a good fit for your family and home. It doesn't matter what breed the dog is or if it's a mix or not. What matters is the temperment of the dog. Does he behave well, nice,even tempered.
The majority of dogs at the shelters are put to sleep if not adopted. Just know that whatever kind of dog you decide to adopt you will be saving! Shelters get so many dogs in everyday and unfortunately they don't have the room or money to take care of them all. So when they start to get full they take the dogs that have been there the longest and put them to sleep. They give them a shot that doesn't hurt and the dogs falls asleep and never wakes up again.
You are doing an awesome thing by adopting for a shelter you are saving that dogs life!!! The dogs know too. They know that other dogs are being put to sleep and they hate being in shelters, they don't have any freedom and have to stay in a cage and don't get much attention. When you adopt for a shelter the dog knows that you saved them. They are grateful and loyal to you for that reason. I know, it sounds stupid but it's true!
A mutt is a mix breed dog. It is a dog that is different types. For example, my dog is part german shepard and husky. He's not one breed so he's a mutt! my other one is part australian shepard and rottweiller also a mutt. You're usually better off with mutts. They tend to be smarter and easier to train and just all around better dogs. Good Luck!!!
Dog pound&vet work experience