I think there is a process that makes Green Tea more healthy than Orange Pekoe, Black and Oolong. I might be wrong though. I read somewhere that the pulverization and fermentation of the other teas (as in bagged teas) causes tanins and something else to be released. Tea is not as flavorful and it is not as good for you.
I am trying to look it up.
The reason Green tea is so good is it is left with larger leaves and is not fermented - just lightly dried. So there are more Catechin antioxidants.
But I do have a tendency to enjoy Earl Grey (black tea I think) the most.