Vedas are the most authoritative and the root scripture from which others are derived. Vedanta is the end part of the Vedas that consist of the philosophical aspects of vedic teachings. Itihasa and Purana show the practical aspects of how people lived in alignment with Vedic teachings. As questions emerged in the society about the practical aspects of vedas, they were allowed to freely question, meditate, debate and determine a common course/understanding. Summary of such common understanding of the practical aspects of Vedas were then documented in the Smriti’s.
Sri Aurobindo Ghose (1872-1950), Indian mystical and philosopher, put it this way: Hinduism is the most skeptical and the most believing of all religions. It is most skeptical because it has questioned and experimented the most and the deepest, rejecting nothing but insisting on testing and experiencing everything. From this come our scriptures and our beliefs: the Vedas, the Vedanta, the Gita, the Upanishads…But the most authoritative scripture is the heart, where the Eternal has His dwelling.
If you are new to Hinduism or exploring it, the best scripture to start with is Holy Gita. However, the most authoritative are the Vedas.
Other reading material:
Relevant videos: 10 min summary on Gita,
Author; Dilip Amin
Location of this post (7d): https://www.hinduspeakers.org/ufaqs/which-one-is-the-most-authoritative-scripture/