Depending on cooking style:

Pompano, Yellow Tail, Walu (aka Butterfish), Tuna, Catfish

The list goes on and on.  A good mess of panfish/crappie or walleye from the river is hard to beat, or blackened grouper, snapper or swordfish.

Fresh fried crappie/bluegill are hard to beat. But i eat alot of catfish also.

impossible to pick just one.

Grilled halibut, swordfish steaks, seabass, ling cod, piranha, peacock bass, the list goes on and on.

It's also hard to beat fresh hamachi sashimi, with a little bit of soy sauce and alot of japanese guacamole.  ;D

Freshwater: walleye, crappie, perch.

Saltwater: blackened tuna, mahi mahi, grouper

Pan fried fillets from a 6lb + bass are my favorite.

Red Snapper

Swordfish

Tilapia

Crappie

Love dorado or grouper sandwiches. Fresh salmon, rainbow trout. When I think of it, I don't think I've ever eaten a fish I didn't like (if it was fresh and cooked well). If I had to choose one, I'd have to say fresh (caught that night/morning) bluefin tuna prepared by a great sushi chef. Add a bit of soy sauce and some very fresh wasabi.

I'm hungry.

Sole, walleye, lake pearch, sable

Sable? Now there's something I don't see very often, out here in the middle of BFE. I miss it. Used to have it for breakfast a couple of times a week, back when I lived in civilization.