I have eaten at all three and loved each one for different reasons.
Cali Grill you can't beat for the ambiance. And yes, if you book so you are eating dessert during fireworks, it's incredible. The food here was very good and the service exceptional.
Flying Fish - my alltime fave restaurant in all of Disney. Why? Both my husband and I both had incredible meals, incredible service, and because it's a smaller resaturant, it was very intimate. Loved it!
Artist Point - good food but when compared with the others, I think it lacks the "wow" factor.
I agree with a PP, I'd go with Jiko!!! Hmmm, maybe that is my favorite Disney restaurant?
Or don't waste dining credits on a signature restaurant and do Sanaa - just did this on Monday night and it is going to be a staple on every trip!!!!