I haven't tried all the legendary po boy shops, but I like Johnny's Po Boys in the Quarter--especially their "surf and turf" po boy, which is roast beef topped with fried shrimp.
My favorite po boy place there in recent years has been Killer Po Boys, but they are not traditional. My favorites there are the Seared Gulf Shrimp or Black Beer Beef Debris. Their pork belly one is also famous and it is very tasty, but it has too much belly fat and not enough meat for my tastes.
And my favorite sandwich in the city in recent years, hands down, has been Le Pig Mac at Cochon Butcher. Two all pork patties, special sauce, lettuce, cheese, pickles, onions on a sesame bun. They nail everything you ever loved about a Big Mac, except with tremendously tasty, house-made pork patties instead of lame hamburgers. I can't
not get it on every visit.