It's not the restaurant, it's the item. Whether at DL or in MK, I must have an ice cream cone each trip. I don't know why, but something about that just makes me feel like I've arrived at Disney. I guess for MK, that would be the Plaza Ice Cream Parlor.
However, having eaten at EPCOT's Biergarten in each of my last two trips, that one restaurant may find its way onto my "must" list if I start going to WDW more often. The funny thing is, the thing I really loved eating the most each time was soup, and I'm not a big soup eater.