Among the locations listed—Australia, Papua New Guinea, New Zealand, and Antarctica—Papua New Guinea has the highest overall population density.
- Antarctica has no permanent residents and is largely uninhabitable.
- Australia and New Zealand both have relatively low population densities compared to Papua New Guinea.
- Papua New Guinea has a higher population density due to its smaller land area combined with a larger population relative to the other countries listed.
Therefore, Papua New Guinea is the correct answer.