Is a higher cocoa percentage better?

It removes sugar and adds cacao. That makes the bar less sweet and more intensely whatever the beans are — including more intensely faulty if the beans were poorly fermented, over-roasted or under-refined. There is nothing left to hide behind, which is why a great 100% bar is remarkable and a mediocre one is unpleasant.

A maker can raise a bar's percentage by adding cocoa butter rather than cocoa solids. That increases the number while making the chocolate taste milder and richer, because cocoa butter carries texture rather than flavour. Two 75% bars can therefore differ substantially, and nothing on the label distinguishes them.

Cocoa flavanols are the compounds the health research concerns, and percentage is not a reliable indicator of them. Flavanols are bitter, and much of chocolate manufacturing is aimed at reducing bitterness — fermentation, roasting and especially alkalisation all reduce them. Two 85% bars can differ several-fold in flavanol content and no mainstream chocolate declares it.

The specificity of the origin claim, whether the maker states a harvest year or fermentation protocol, the ingredients list, and how the bar looks and snaps. Those tell you about care taken. The percentage tells you about sweetness.