Australia must protect Australia's interest.
The free movement of trade through the South China Sea is in Australia's interest.
A slice if the resources pie in the South China Sea is in Australia's interest.
Not allowing its self to be bullied by a far greater power is in Australia's interest.
As for which side we would choose. Australia is a free egalitarian open nation. China is a fundamentally corrupt closed nation, which does not allow freedom of expression or freedom of speech. China does not allow political descent. China does not allow foreign ownership of its land.
China has not always and probably will not always be Australia's major trading partner. Backing China in this dispute would alienate Australia from the rest of The rest of Asia From India to Vietnam. I dare say the Russians would be more than a little peeved as well.
Australia has to make a big noise on this issue, as do all of the other smaller Nations because it is in our best interest.

