I use and recommend the Macquarie Dictionary for spelling. The Australian Government and universities consider this work the authoritative source on Australian English. By using this work as your spelling standard, you adopt a consistent strategy, which readers will respect.
Usage of the Macquarie Dictionary
The Macquarie Dictionary is available as a printed book, an online website, and as an app. Only the online edition is updated annually.
While I have both the Macquarie Dictionary app and the printed book in my office, I tend to use the app more than the book. This is mostly because looking up a term is much quicker on the app. The app also provides related words or terms when using the search function. I also love the list of ‘recent’ words, which saves all recent searches. Of course, the app is much easier to carry around and very handy when working away from my office.
However, for comparing definitions and for terms with large explanations, the book is more convenient. So, really, having both is the best option.
You can find an overview of the history of the Macquarie Dictionary on Wikipedia here.
The online edition is available for a 30-day free trial at the Macquarie Dictionary website. However, subscription to the online version is only for one year and needs annual renewal. As this costs more than the app (which is not updated annually, but still very good), I have not used the online subscription.
To find other recommended resources for writers and editors, check the resources page.