It’s a good thing that Franco-American relations don’t depend on chocolate, because if they did, diplomats would have their hands full. In America, the preference is for milk chocolate; in France the national sentiment is the darker and more bitter, the better. Of course you can find milk chocolate in France, but when you do, it’s darker and richer than what we get here. I’m a fan of bittersweet chocolate and that’s my go-to chocolate for baking. If you like a milder chocolate, you can substitute semisweet. However, unless the chocolate in the recipe is used like chips, I wouldn’t advise swapping milk or white chocolate for dark chocolates; the lighter, milkier chocolates don’t behave in the same way as their darker siblings, and you’re likely to throw off the results.