It depends on where I am, but generally it's probably octopus for me. That assumes I'm at a restaurant I deem knowledgeable about cooking it. Oysters are right there as a close runner up.

The safe choice (let's say I'm in Kansas but want seafood and it's not a top class seafood place) for me is shrimp.

To the OP - I love grouper too, especially grilled, good choice. And walleye is excellent, especially for a Friday fish fry. If you haven't had fried Perch (WI, IL, MI, etc.) give it a try next time.