Dark Chocolate has many antioxidants, the antioxidants known as polyphenols and catechins.

The polyphenol families of procyanidins & epicatechins are strong antioxidants also found in many plants and vegetables including red grapes & wine. Proanthocyanidins play a role in the making of collagen & elastin and can lead to a stronger circulatory system. Proanthocyanidins are also shown to speed up recovery from plactic surgery. http://en.wikipedia.org/wiki/Proanthocyanidin

Catechins, in particular epicatechin found in dark chocolate, can reduce the risk of four of the major health problems: stroke, heart failure, cancer and diabetes.
http://en.wikipedia.org/wiki/Catechins

Milk Chocolate has no antioxidant activity due to milk binding the antioxidants. To take advantage of the antioxidant activity of chocolate you need to have 70% cocoa solids and no milk.
http://www.med.umich.edu/UMIM/clinical/pyramid/chocolate.htm

http://dangilliland.wordpress.com/2008/06/07/dark-chocolate-vs-milk-choc...

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