I had a small egg business for almost 10 years. At the most we had 200 hens +/- a dozen or so. We used pretty much all Red Sex Links. We were extremely lucky to break even with the egg sales, but it was more of a hobby than an actual business. We suffered a lot of predation issues even with roosters. We learned quickly that roosters die quickly to hawks, foxes, racoons, etc. The best defense is hiding cover and swift reaction times from the hens. The roosters would at least give warning to the hens.
The Production Hybrids like the sex links, ISA's, and production reds, are hard to beat for egg laying. I have no experience with Australorps to compare them. I did not do any trap nesting to measure egg production, but the birds layed very well. Even in winter we were getting a good number of eggs.
If you are strictly wanting brown eggs then the Leghorns will not fit, but if white eggs are not an issue the Leghorns are hard to beat. If I were to start another egg business, it would be all Leghorns. They are thrifty on feed, forage well, and are quick and agile compared to the heavier breeds we had in the past. All of which will add to the bottom line when it comes to an egg business. The profit margin is not that large, and every ounce of feed cuts into it.