I've by no means had a lot or even enough to really have much opinion but I've always really liked the gumbo at Benno's on the seawall @ 12th. I love that place. For simple fried seafood it's perhaps the best on the island. Their gumbo is really good too.
I've also tried the 646 Gumbo bar and I can verify that it is bad.
They use the same roux for every variety! You want a chickena and sausage gumbo, here I'll add some chicken and sausage to it. You want a seafood gumbo? Here I'll add some crab and shrimp to it.