The best salmon I've had at Disney was at Brown Derby.
Grilled loch duart salmon, over greens with peaches and blue cheese, with a fig and honey sauce/dressing. It's slightly different now, as the sides are seasonal, looking at the last updated All Ears menu, right now it comes with sauteed autumn vegetables and blue cheese polenta cake.
The cedar plank-roasted salmon at Artist Point is also very good. Suprisingly, the other salmon dishes I really liked have all been at buffets, and I can be very picky about buffet food sometimes since some I think lack quality, but Crystal Palace, Tusker House, and Boma, have all had very good salmon.