Australorp isn't an Orpington, though I believe the Orps were used in the creation of the Australorp breed, if I'm not mistaken.
You mean temperment, egglaying, etc, between the different Orpington varieties? I have Buff Orpingtons and I raise Blue/Black/Splash Orps. They are all very nice, very large birds, extremely fluffy, especially the breeder quality Orpingtons. If you breed blue to blue, you have the possiblity of getting blue, black or splash chicks, so all those would be similar, I feel, in their traits. My Buff Orps and Blue Orp girls are all good layers, with the Buffs I have, both hatchery girls, being very productive. They are all sweet, non-aggressive birds, too.
Pick what you like! Can't go wrong with Orpingtons.