Muckdog pointed out that it was in the news recently that coffee is America's greatest source of antioxidants.

"Americans get more of their antioxidants from coffee than any other dietary source. Nothing else comes close"

Black tea was the second-leading source of antioxidants in the U.S. diet. Bananas, dry beans and corn placed third, fourth and fifth

Roasting supposedly enhances antioxidant activity and may even give it four times the amount of antioxidants as green tea!
Keep in mind though, that coffee can elevate cholesterol levels while green tea helps lower them. Coffee also has more caffeine than tea: an average 6-oz. cup of green tea contains about 30 mg of caffeine, coffee has about 100 mg per cup.