This seems better suited to r/askphilosophy; r/buddhism is also a large subreddit that may be useful for your enquiries about Buddhist texts

Are the Dhammapada or the Upanishads the main writings for hinduism and buddhism?

Simply put. No.

The Dhammapada and Buddhism

The Dhammapada is a very short book of poems that are supposedly the distilling of the Shakyamuni's teachings. In actuality, it is a very small selection taken from one of the Nikayas in the Pali Canon.

The Pali Canon, i.e. the Tipitaka (Sanskrit: Tripitaka) is the collection of scriptures said to be lifted directly from the Buddha's teachings, but was preserved orally until the first century BCE when the Fourth Buddhist Council finally decided to set it down to writing. I believe it was Thich Nhat Hanh (in my own 2001 copy) who said that the whole of the Buddhist canon could be lost as long as the Dhammapada is preserved, then the Buddha's teachings will survive, then compares it to the "Sermon on the Mount for Buddhism." (I will come back and source this shortly when I head back home in a couple of hours.

That said, the Dhammapada is very poetic, and while I'm sure it can be argued that it is the teaching of the Buddha, to use it primarily as an academic work itself for what Buddhism teaches is painfully limited and small. Gedun Chophel, the Tibetan artist, scholar, historian, and libertine translated the text himself into Tibetan, appreciative of its poetry. However, Gedun Chophel was once a trained monk and was probably attracted more to the simplicity and meditative ideas behind the poetry, aware that the monastic discipline, doxology, and complex history of Buddhist philosophy and debate was lost (which is probably what drove him away from the monastery in the first place).

The Upanishads and Hinduism

I am not a historian of Hinduism, but I can address that like the Dhammapada, they are clearly ripped from their context if you read them on their own without any foreknowledge of the Vedas or Puranas.

are the Dhammapada or the Upanishads the best east philosophy works out there

This is fundamentally a question of opinion. I'm sure Chinese, Japanese, and Koreans will probably take issue with the assumption that the "best east philosophy works out there" are only found in India. And since they are fundamentally works of poetry, I think their philosophy would be somewhat in doubt since there are many other words of explicit philosophy (i.e. the Madhyamikas and Yogacarins) out there.

another anon said to understand the Dhammapada you need to read the Pali Canon and the Mahayana sutras or you are not grasping the philosophy behind the sayings.

The original Dhammapada is located in the Pali Canon which is the holy canon of Theravadin literature. It is theoretically available in the Mahayana Chinese canon, though we're zooming out of my area of expertise at that point. I know for a fact it is not located in the Tibetan canon, the Kangyur.

Like anything written, it's not necessary to know the entire history of the book to gain something from the text, but as I described above, you will be missing the context of Buddhist philosophy, history, monastic discipline, and doxology. Since none of it is really present in the text. If you want to actually learn Buddhism, think about broadening your horizon to a different set of texts (i.e. Andrew Skilton's A Concise History of Buddhism, Taranatha's History of Buddhism in India, Bu-ston's History of Buddhism, are three good options). If you want to appreciate early Buddhist poetry in translation, this could be an ok place to start.

For the Upanishads if you don’t read the Vedas and Puranas you will not understand it.

Upanishad literally translates to "sitting near [the teacher]." The first writers and scribes of the Upanishads would have been well versed in the Vedas (the epics) and the Puranas (the instructions). And the first audiences of the Upanishads would have some working knowledge of them.

In the end, it all really depends on your goal. If you want to read them and gain some kind of spiritual knowledge, appreciate poetry, or just learn something new or different, feel free. But if you're looking to learn about Hindu philosophy, history, or literature, I would recommend avoiding them and starting with John Keay's India: A History.