The longer the fish travels to spwan the more fat content it is going to have. Springers and summer chinook usually travel the farthest for salmon. Summer steelhead might not travel far, some do, but they spend lots of time in the fresh water so they have a higher fat content. When it comes to fall salmon, if you catch them in the ocean it's tough to tell the difference between the different fish. Once they get close to the rivers though it all changes and they start loosing their quality.

Also it all depends on how the fish was handled and how freash it is. If you keep the fish cold from the moment you kill it, and BBQ it that day or the next, nothing can compair to it. But if you leave it on the bank for a few house, freeze it, then eat it, the fish will not be as good.