* Both American and Australian English are varieties of English. They share a common ancestor (Early Modern English) and have a lot of similarities in vocabulary and grammar.
* They're both considered "correct" within their respective countries. Neither one is inherently superior or more "correct" than the other.
Think of it like this: Imagine you have a family tree. You and your cousins share the same grandparents, but you've all gone your separate ways, developing your own unique personalities and ways of doing things. American and Australian English are like cousins in the English language family.
So, the answer is neither American nor Australian English is "better" or "more correct." They are simply different dialects of the same language.