Well if you really want some chocolate high in anti-oxidants and you aren’t averse to eating things that don’t taste nearly as good as some of the bars people talk about on seventypercent, then you could always stock up on the Mars ChocoVia product.
They have one that is not a snack bar, but is actually a box of dark chocolate bars. As I understand it, they have spent considerable money, and a number of years, trying to figure out how to process cacao to minimize the loss of the anti-oxidants and provide consistent anti-oxidant levels in their products.
I don’t have any scientific data on what difference there is between their product and other dark chocolate, but you might find something on-line.
Actually, while searching around I found some interesing things, but the information is all provided by Mars, so it is anyone’s guess about how much is marketing and how much is reality. The last link is unrelated to the current topic, but I found it interesting:
Also, as Oz_Choc, and perhaps Sebastian, have pointed out before, Forastero cacao has higher anti-oxidant levels than other cacao and you will notice that chocolate higher in anti-oxidants will be slightly (or even vastly) more bitter and astringent than something like a Porcelana bar.