Majority of Australians approve Same Sex Marriage, page-118

"Just as an aside, if two couples equally met the requirements to adopt, would it be right or wrong as a tie breaker to give more weight (however slight) to the married couple as opposed to the unmarried couple?"

That's not up to us, but the appropriate authorities. All things being equal, there should be no difference. But in the current society a case could be argued that, without any other considerations, the child with hetero parents would be less discriminated against, at school at least.