Determining which faith has strayed the least from its original beliefs is complex and subjective, as it depends on how one interprets "original beliefs" and what is considered a deviation. Most religious traditions have evolved over time, adapting to cultural, political, and social changes. That said, here are a few perspectives on how different faiths view themselves in relation to their original teachings:

1. Islam

• Argument for preservation: Many Muslims believe Islam, particularly in its Sunni form, has stayed closest to its original teachings. The Quran is considered the literal word of God, and has remained unchanged since it was revealed in the 7th century. Furthermore, the Hadith (sayings of the Prophet Muhammad) and practices like Sharia law aim to keep the faith aligned with its origins.
• Traditionalist sects: Groups like the Salafis emphasize strict adherence to the practices of the earliest Muslims (the "Salaf"), believing that Islam in its purest form was practiced by Muhammad and his companions.

2. Judaism

• Argument for preservation: Orthodox Judaism maintains that it adheres closely to the laws and teachings of the Torah, the foundational text of the Jewish faith. The Oral Torah (Talmud), which dates back to ancient times, plays a key role in interpreting these laws, and the practice of rabbinical debate is seen as a continuation of traditional methods of understanding the text.
• Diversity: While Orthodox Judaism claims fidelity to ancient practices, other branches like Reform and Conservative Judaism have made significant adaptations to modernity.

3. Eastern Orthodox Christianity

• Argument for preservation: The Eastern Orthodox Church views itself as the unbroken continuation of the early Christian church, particularly the traditions established by the first seven ecumenical councils. They emphasize maintaining ancient liturgical practices, the Nicene Creed, and other core aspects of early Christianity without much innovation.
• Minimal changes: Unlike Roman Catholicism, which has seen more doctrinal development (e.g., the doctrine of Papal infallibility), Orthodox Christianity sees itself as a faithful continuation of early Christian tradition.

4. Zoroastrianism

• Argument for preservation: As one of the world’s oldest monotheistic religions, Zoroastrianism has experienced relatively few changes in its core beliefs and practices. Zoroastrians continue to emphasize the worship of Ahura Mazda, the cosmic struggle between good and evil, and fire as a symbol of purity, much as their ancestors did thousands of years ago.
• Preservation through small numbers: The relatively small size of the Zoroastrian community may have helped preserve its traditional practices, though modern Zoroastrianism also faces challenges of adaptation.

5. Sikhism

• Argument for preservation: Sikhism, founded in the 15th century by Guru Nanak and solidified through the teachings of ten successive Gurus, is relatively young compared to other major world religions. Sikhs believe that the teachings in their central text, the Guru Granth Sahib, have remained consistent with the original message.
• Faithful to the core: Sikh practices like community service, equality, and monotheism have remained fundamental to the faith since its inception.

6. Hinduism

• Argument for preservation: Some schools of thought within Hinduism, particularly those that adhere to the Vedas and ancient texts like the Upanishads, claim to practice traditions that are millennia old. The ritualistic, temple-based practices in many branches of Hinduism are seen as continuing ancient traditions.
• Diversity of practice: Hinduism has also been incredibly adaptive, and its multitude of sects and philosophies make it difficult to say that one specific strain has "preserved" the original teachings above others.

7. Roman Catholicism

• Argument for preservation: Roman Catholics believe that their doctrines have evolved but still reflect the original teachings of Jesus and the apostles, especially through traditions like apostolic succession. They see the Church’s ability to develop doctrine as guided by the Holy Spirit, making it a faithful extension rather than a deviation.
• Counterpoint: The Catholic Church has seen significant changes and reforms over time, such as the Second Vatican Council in the 1960s, which some see as departures from earlier forms of the faith.

Conclusion

Many faiths claim to have preserved their original beliefs closely, but each religion has experienced development over time. Some traditions, like Eastern Orthodoxy, Salafi Islam, and Orthodox Judaism, emphasize adherence to early practices. However, the degree to which any religion has changed is influenced by how one interprets doctrinal evolution versus core belief preservation.