I've had all three of those breeds over the years, and if you are not going with all three breeds, then which two breeds you should go with depends on what your objectives are with your hens. If egg production is a priority, then I would not cut out the Australorps as they are the best layers of the three breeds. If you love beautifully colored eggs, then I would not cut out the Welsummers as their chocolate eggs (at least in my personal opinion) are the prettiest eggs in the chicken world. If you want calm and gentle birds then I would keep the Orpingtons and Australorps which are easily made into lap pets. Depending on where you live, the climate could also play a factor in your decision. All three breeds are very cold hardy, but Australorps are more heat hardy than the other two breeds. Whatever breeds you keep, you need to make sure that they are approximately the same age and size or the smaller ones will be bullied, perhaps even fatally by the larger ones. Whatever breeds you decide to go with, good luck with your flock.