So many websites have listed L'As du Falafel on rue des Rosiers (4th arrondissement) as the best place for falafel. Even the New York Times had their article saying it was the best in Paris. Of course, I had to check it out myself. So today I arrived a little after noon. I normally would take the sandwich to go, but I took a seat with my friend inside. The service was quick, but I think, confused. We each got the falafel special sandwich (with eggplant), but for some reason, our sandwiches had very different ingredients, and mine was missing my eggplant which I had to holler for. She had tomatoes, cucumber, and eggplant, and mine had some different cabbage slaws. The falafel itself was fine, but nothing special compared the other falafel in the area. The slaws were lacking in flavor and the eggplant skins were quite bitter compared to other restaurants'.
My expectations were maybe too high, but the falafel at L'As du Falafel is nothing exceptional. Hannah's is quite good, and one of my favorites is from Chez Marianne. My best may have been from a Lebanese restaurant on rue Montorgueil (I can't remember the name -- I was there over a year ago). I'll look for it again.
There's a new falafel place almost right across from L'As du Falafel. It had a very odd, Japanese-sounding name. There was a fifteen-foot line of patient high-schoolers waiting alongside the restaurant. Maybe that's where we should all be eating. The sandwiches from all these places are about the same price (to go), 4-4,50 euros, so they're not there because it's cheaper or anything. It's likely these kids have tried all the falafel in the Marais and had decided that this one is the best.
I'll get back to you after I do some more research.