The best container is ceramic. Glass is okay. It is important that your teapot has a lid. Materials to avoid include cast iron or metals. Chinese herbs can interact with these metals casing chemical reactions that can alter the therapeutic qualities of your herbs, or worse yet, have an unhealthy effect on whoever drinks the tea.
Stainless steel is better than the other metals.
Teflon coatings are not as good as ceramic coatings. In ancient times the source of the water used in the tea was an important issue. Some teas required water from a spring, others called for water collected during a rain. Nowadays, any drinking water is acceptable. The purity and cleanliness of the water you choose is a personal choice.