First of all, if you are busy in school, I really don't recommend any of these breeds. All of them need a job, and the job requires a high level of commitment.
What happens if you get involved in extracurricular activities? What about your social life? These things interfere with a commitment to a dog like these, and can be problematic.
Not all herders are also protection dogs. The ACD is NOT a protection dog, unless you want anyone who enters your home to be....lunch.
As far as the breeds you have listed, I can tell you right off that the ACD is NOT a good choice for a pet, and should not be kept as a pet. This breed was bred to work, and nothing else. If you have no experience with this breed, I strongly urge you cross out this choice on your list.
The ACD is very smart, and bred to work independently, so they have an intelligence level that will challenge your authority if you are not a strong owner. They were bred to use their teeth on everything, and bite inhibition is a very difficult thing to teach them They are fearless, and aggressive. They are also very territorial as they mature, and your neighbors and relatives may not appreciate being grabbed by the leg and dragged "to the chute", like the other steers.
They have a horrible reputation with small children, going so far as to bite them because of the way they move. If your neighbors have small children, this is a real problem.
When bored, the ACD rivals the adolescent Wolfhound in its destructive capabilities, everything from eating your home to biting you and everyone else in the house if the dog is frustrated enough.
They are not known for being good with other dogs. ACDs have no use for other dogs. All other dogs get in the way of them doing their job, and could be attacked for interfering with the frisbee toss in the local park.
While obedience is always a good idea, it can never stop with an ACD. What are you going to do next when your dog learns heel in 5 minutes and looks to you for the next job? And what are you going to do when the dog refuses to respond to the command because you have practiced it too much in the last 10 minutes?
I live in the dog community, and work with many shelters and rescue groups. The ACD usually is euthanized as soon as it hits the shelter, because they can never pass the temperament test. In the no-kill shelters, they tend to live out their lives there, as the longer they are caged, the more aggressive they get, until no one can work with them.
ACD rescue will not accept a dog with any kind of bite record, or any dog that seems fearful and unsocialized.
ACDs are on many BSL lists in communities all over.
The Australian Shepherd would be a better choice, but also NOT a protection dog. However, the personality is usually more mellow, and this breed is also very smart and easy to train to do all kinds of things. I recommend you find a GOOD breeder who pays attention to temperament.
Borders are too intense for the first time owner in my experience. And the amount of behavior issues stemming from bad breeding are legion.
As far as the GSD, I wouldn't recommend that breed to anyone right now, having seen so many bad tempered dangerous animals with severe dysplasia.
Only know a few Malinois, but any of them would think you were quite tasty and would watch you like a hawk for the opportunity to strike.........
You would be the toy.
Owner of a rescued ACD. Starting competition obedience training this fall. She learned everything else already. She has a three bite record, all humans. Also owner of a rescued Aussie. He is in training to be a therapy dog, with his great temperament. Active volunteer with Aussie rescue.