My inclination is to say the Yachtsmen Steakhouse at the YC, too. But really, that's perhaps the best meal I've had at Disney, but I expected it to be good.
So I'll probably get shot for this, but the meal that most surprised me was some lousy piece of grub I got at Pleasure Island at 1 AM. I was tired, hungry, the wife was yelling that my designated driver was leaving in two minutes with or without me, and I didn't want to eat vending food at the hotel. I grabbed some greasy looking sausage sandwich from a cart and man, that was the best sausage sandwich I'd ever eaten. Maybe not cuisine haute, but decidedly the most surprising meal I've ever had on Walt Disney property.
Pat