Overall? There isn't just one! The CS/QS restaurants in the resorts that are great are so for different reason, so picking one (at least for me) is not possible!
Boardwalk Bakery (BWR)
Boardwalk To Go (BWR)
Capt. Cooks (Poly)
Geyser Point (WL)
Landscape of Flavors (AoA)
Mara (AKL)
Pepper Market (CSR)
P&J's Southern Take Out (FW)
Roaring Fork (WL)
Sassagoula Floatworks (POFQ)
Siesta's (CSR)
We love the food court at POR. When we stay at OKW, we often drive to POR for the variety in the food court. We also went to AKL, Mara, one time and really liked it, but that one can get VERY backed up at meal time.
Sassagoula Floatworks at POFQ is definitely the best hotel qs restaurant. Grab some coffee and beignets and then take a seat outside and you will swear you are in New Orleans.
I enjoy the QS at Riverside too!! I was at CSR and I don't like their options - maybe it's because their food court is currently undergoing refurbishment but I wasn't all that impressed. I also like the Poly's quick service.
Not to split the baby a dozen plus ways but I suspect every food court has at least one entree or dessert that will blow you away, the trick is having the time in each food court necessary to find that item or those items.