I have a mate who use to work in a canning factory and every now and then they would get a few Patagonian Toothfish in their nets - he reckons that was in a league of its own.
My personal favourite game fish is Dorardo - always a winner, no matter how you cook it. Wahoo is also quite good. Couta isn't bad either.
As for bottom fish, like Reefman says, you can't beat a rockcod, and the best rockcod in my opinion is a swallowtail rockcod.
Smaller kabeljou & geelbek makes the best curries.
YFT is dry but I guess okay on a braai or in a salad!
Butterfish gives me the runs!
Gilly