I happen to like green tea over black tea. Green tea contains the antioxidant epigallocatechin gallate (EGCG) which has been shown to have anti-inflammatory activity through the inhibition of nuclear factor kappa B (NF-kB). NF-kB is a transcription factor which is activated in the cytoplasm, enters into the nucleus, and then binds to DNA inducing the transcription of proinflammatory cytokines.
Here's some background information. Green tea comes from the same plant as black tea. However, leaves picked for the two teas are processed differently. In effect, leaves for the production of black tea are allowed to ferment while leaves picked for green tea are steamed and then allowed to dry. The fermentation process in black tea consumes much of the antioxidants present in the leaves converting stronger antioxidants into weaker forms and it also reduces the overall quantity of antioxidants present. The application of heat via the steaming process in the production of green tea neutralizes the enzymes present in the leaves which are responsible for fermentation. As a result, green tea has a higher level of antioxidant activity.
One drawback is that the tea plant, Camellia sinensis, concentrates fluoride which can cause bone problems in high doses. You may be interested in reviewing the following thread for more information on this problem.
In general, I think that 4-5 cups per day of a high quality green tea should not be a problem. The people discussed in the Mayo Clinic research article were consuming considerably higher quantities.
A good introductory book on green tea which is well referenced is Green Tea
by Nadine Taylor. There is also a plethora of published papers available through PubMed.
One last note is that green tea contains less caffeine than black tea and has about 30% of the caffeine present in drip coffee. In addition, the presence of the amino acid theanine in green tea provides for a calming effect further reducing the likelihood of getting caffeine jitters from a modest consumption of green tea.
A search of the forums should produce several posts discussing the benefits of green tea and EGCG.