Is regular green tea better for you than diet green tea if so why do diet green tea have something in it that regular green tea don't?

Yes and No: It sounds like you are discussing sweetened beverages. So "diet" green tea would be sweetened with an artificial sweetener with no calories and "regular" green tea with a sugary sweetener with calories. Which is better? Why not drink unsweetened green tea which would be the best choice. Green tea is rich in antioxidants which many believe is good for us.

Forget green tea: Green tea is the latest in a long line of overhyped nutritional products. Claims include weight loss, better health, longer life, better endurance. Do not believe the hype. Yes green tea contains some anti-oxidants and phytonutrients, but it still contains caffiene which is a stimulant and has duiretic properties. Too much green tea is not good for you.