cocoa and flavonoids

If cocoa has health benefits, how do I maximize those benefits? Obviously hot chocolate mixes full of added sugar are bad. Is there a brand I should buy that maximizes flavonoid content?

UPDATE: I'm drinking (what I think is) unprocessed cocoa now, sweetened with sucralose, and dissolved in hot water with a little skim milk. It's a bitter taste, different from chocolate, but I can get used to it, just like getting used to drinking black coffee or unsweetened tea.