Which wines have a strong, bitter flavor?
I haven't cooked chocolate with regular wine per se, but my instinct is that to get the right marriage of flavour you really might need to consider alternative approaches with both a higher sugar and alcohol content: dark chocolate is a very powerful flavour that will obliterate most wine.

So I would try using something else wine-related but with a considerable higher sugar and alcohol content: Port and chocolate certainly can complement each other well - I would recommend a tawny port (I have used this combination as a sauce for a savoury dish). You might try sherry too, but this is slightly riskier territory in my opinion.

A further alternative depending on the dish you are cooking would be to pursue your current course add a third component that will help with the overall flavour structure, typically something bittersweet and with fruit, such as redcurrant jelly.