I grilled fish last night and as I was explaining different parts to my kids, they asked "what is your favorite part"? I heard numerous times from cook's tour and no reservations, Anthony Bourdain talk about the collars or the cheeks. Those are good but I think the best part of any fish is the belly flap, the soft fatty underside of any fish tends to have more fat and flavor and cannot be beat for tenderness. To me (not counting flat fish), the belly area beats cheeks and collars hands down.

Fish shanks are delicious.

Fish roe. Mmmmmm.......

Maybe it's the preparations rather than the parts, but I'm going to go with collars. I like toro well enough, but simmered yellowtail collars? So rich and satisfying.