That’s really a matter of debate. Internationally, the most appreciated dish from France seems to be the boeuf bourguignon.
Within France, the most universally appreciated dish might be the Raclette, but at best we share the pride of this delicious meal with the swiss (and at worst, they own it and we just copied it).
So I’d say that the best dish in France that is a traditional dish in at least one of the current french region is the crêpes, and more precisely the galettes au sarrasin.