I have had sushi at Cali Grill, Kimono's Wolfgang Puck's and at the sushi bar in Epcot.
The sushi at and CG was the best - some of the best I have had anywhere! It is also so much fun being up at the top of the Contemporary, especially when the MK fireworks are going off! The sushi at Kimono's was top notch as well. We enjoyed the sushi Epcot too, but the best overall experience was Cali Grill, hands down, especially if you are into wine.
We had sushi at Wolfgang Pucks twice. The first time, it was fantastic, but the second time wasn't so great. There was one piece of shrimp that smelled like a combo of mold and ammonia. It was just not fresh. I think that, along with the reaction of the manager ("you are the first one ever to complain about our sushi!") totally turned me off the whole place. I mean, come on, everyone knows that when shrimp smells like that, its bad! Our first experience was so good though, that I am willing to say it was probably an isolated incident.