The one thing that would make me keep one of the barred rocks, instead of one of the australorps, is if you are planning on a mixed flock of various breeds anyway and one of the BRs is a much better rooster.
Some roosters are really great and some roosters are not, from a behavioral standpoint. They have different instincts and temperaments. If I had one that was good to the hens, watched out for the hens to keep them safe and was good with people, I would keep that one. If I had one that was rough on the hens, didn't protect them or was extremely aggressive to people, then he'd be going to freezer camp.
Sometimes you want to choose based on what breed they are, sometimes on what they look like or how well they match the breed standard, but sometimes it's how they behave that makes your choice.