Don't forget about Christmas Island and Cocos/Keeling Islands
As others have noted, the question is very very broad. It's like asking for a full report and comparison on each of these islands, while you offer no details as to who you are or why you want to know. Knowing your audience is an important part of forums like this. Of course some will type novels and maybe you'll get one of these people, but otherwise it feels like a waste of time for most. The 'main differences' between these islands are easily researched. The subtleties of each destination, once you've gone that far, is what makes this forum great.
Australia is a big place and these islands are remarkably different from each other. It's not like asking the Chef what is on the menu. It's like walking into the Grocery Store and saying, 'what do you like to buy here?'
I've been to most of these islands, but preference is subjective. I am happy to answer more specific inquiries.