We just tried, for the first time, both 50's Prime Time Café and Whispering Canyon. Haven't tried Garden Grill
I didn't care for the loud server interaction at WC (not my cup of tea). They were joking around with customers much more (and louder) than I care for. My husband, however, loved this aspect. The food was fab!!! Some of the best food we have had at WDW, to date. Very sexy food, not at all standard or stodgy. I would put up with the atmosphere again in a heartbeat!
50's the server was much more tame. The menu and food weren't memorable. They weren't bad, just not memorable.
We also like to try resort restaurants in order to see the resorts, but if we are in a park and staying there for a while, we'll go to a park restaurant (like 50's Prime Time).
Let us know what you decide!