The three main types of tea, Green, Black, and Oolong, are all derived from the same plant: Camellia siensis. The only significant difference is how they are processed before being brewed. In all cases, tea has antioxidants called polyphenols (like in red wine) which are believed to improve health in several areas. Green tea, because of its processing, is believed to be the highest in antioxidant levels.
Epidemiological and clinical studies around the world have found at least tentative health benefits in preventing cancer, improving cholesterol numbers, preventing atherosclerosis (hardening of the arteries), improving digestion and reducing bowel diseases, preventing and controlling diabetes, and (of course) boosting weight loss. The studies have been highly variable, and largely owing to the complex and inconsistent nature of a natural substance such as tea, the results must be taken with a grain of salt. Still, considering that tea is one of the most widely available drinks in the world, it would not be a difficult endeavor to perform your own experiment to see how green tea might benefit your personal health.
The Red Diamond company gave every Khantestant a box of their green tea to try during the contest. I do not partake of any teas for religious reasons, but I thank them for the offer. I gifted my box to a coworker who regularly drinks tea and he said it was good.