To determine which part of "The Maori: Genealogies and Origins in New Zealand" best shows that the Maori value freedom, we should look at the motivation of the brothers. In the context of the Maori creation stories, the conflict between Tû and Tawhiri, as well as the resolution following Tû's wrath, reflect various aspects of freedom, but the underlying motivation for Tû's actions—his desire to create a world where beings could live freely and thrive—emphasizes the importance of freedom in Maori culture.
Thus, the motivation of the brothers is likely the best part that highlights the value of freedom among the Maori.