Aussies range from 45 to 85 pounds. So not all are smaller. Breeding is all over the place as far as coats and sizes. There is no standard weight for Australian shepherds. My one is 50 pounds and my other is around 80 pounds, my last show bred Aussie also was around 80 pounds.
Most are smart but without enough exercise some can be a pain. I follow a few Facebook groups and lots of complaints about them barking, biting, and generally being trouble. They can be frustrating to housebreak too for some reason.
It pays to know the worse as well as the good. They are definitely a challenging breed sometimes, but they are also good dogs.
From your list of breeds the retrievers will be the most biddable, they are bred to work with humans. Aussies are the most clownish, they are bred to think for themselves which sometimes can be challenging, and terriers can be the most stubborn, and are more prey driven, but there are different degrees of terriers. All 3 choice can be big barkers, and destructive when young if not exercised well.
Either choice will keep you busy for a year or two as they mature and settle when gotten as puppies.