Best Authentic Vietnamese Pho in Paris
Pho 14 on avenue de Choisy is still my fave, but it tends to be good and bad alternately.
Song Heng on rue Volta has good broth - which is my number one priority in pho - and, not top priority but an even greater rarity, good meatball. Very no-frill place. You queue outside for a table. As soon as you are finished, you are expected to pay immediately. In fact you must get up to go pay in order to be out of the small restaurant faster.
Lastly authenticity is a word like the horizon. It is always further out, out of reach, unless you are in the middle of nowhere in the outskirts of Hanoi.
Ditto the word Best. To be qualified to use the word "best", one must have tried all the phos in all of Paris. I certainly am not qualified. I can only cite a couple of my favorites above. Hope it helps.