With American and Australian English, the languages are the same. Any American should understand the basics of anAustralian's written or spoken communication, and an Australian should have no trouble understanding an Americaneither. However, there are some subtle differences in the common usage of grammar, phrases, and words that might behelpful to learn.
Australian vs. American English
More like British, Australian English speakers are more likely to say "shall." In other words, it would be common to hear an Aussie say, "I shall return." You would almost never hear an American say that unless they were trying to sound upper-class and fussy. It would be more common to hear an American say, "I will return" or "I'll return."
Similarly, an American would ask, "Should we do this thing?" On the other hand, a native from Down Under might ask, "Shall we do this thing?" Of course, either would understand the other, but there is a difference in common word selection.
The Oxford comma is one debated punctuation mark. However, Australians are more likely to use the last comma. For example, a list like eggs, bread, and milk would have a comma before the last conjunction.
In this case, the conjunction is "and." However, some American styles, particularly AP, omit this last comma unless the sentence might be difficult to understand without it. In this case, the list would read: eggs, bread and milk. For everyday writing, this is more of a preference and it can be subjective. However, Australian grammar is more closely related to British grammar where the Oxford comma rules. Also, some American styles do use it, but it is commonly omitted in the news or other publications that adhere to a strict AP style.
Americans write favor and color, but Australians are likely to write favour and colour. At some point, American English omitted that extra "u" that was introduced in British English.
Is Australian Or American English Better?
Obviously, it is better to write to Australian standards for an Australian audience. This is particularly true if the writer is trying to appear Australian. If an Australian audience knows the writer is an American, they will probably overlook style differences.
For international English exams, either style is probably acceptable unless stated otherwise. This is a good thing to find out before taking the exam. While either style might be fine, it is also best to remain consistent. In other words, if Australian phrases, grammar, and spelling gets used sometimes, it should get used all the type. The same is true for American grammar. Consistency is a good rule to follow at all times.
Otherwise, neither slight variation of the language is better or worse than the other. They are just the standards that are commonly adhered to in order to make communication clear from one speaker or writer to the next. Though there are some differences between Australian and U.S. English, they are not so distinct as to make the two versions different dialects or languages.