I think green tea is often overemphasized in terms of its health benefits. Check out this study:
This study compares many different types of tea, including many different green and black teas, as well as other types of tea including oolong tea and various herbal teas.
The results are interesting...there's a huge amount of variation in the total antioxidant content from one tea to the next...and the actual chemical makeup varies greatly between teas with a similar total content...some have more of one chemical whereas others have more of another. Also...scientists hardly know if they're even measuring all the chemicals...certain teas may not have any of the chemicals that they were looking for...but there may be other ones yet to be discovered.
What is the lesson to be drawn from this? Don't jump to conclusions that green tea is automatically better for you...and don't ignore other kinds of tea such as black tea! Most tea is good for you...and some teas are much better for you than others. Green tea may tend to be better, but some black teas are probably better for you than some green teas...and within any type of tea, some teas are much more beneficial than others! And most importantly, we don't really understand more than the beginnings of the health effects of tea...