I've eaten at three:
50's PT - consistently great food, huge portons, fun environment esp for families, service has always been good but you may or may not get a playful waiter. Point is that you're at mom's house and are supposed to be treated as such but some waiters dont' get into the act. Can be disappointing if you want that, others are relieved they aren't picked on. We've loved the homecooking here regardless
SciFi - for lunch, it's a good burgers and shakese place. For dinner, DH had a good shrimp pasta but my catfish was very bland. Environment is VERY cool, best themed restaurant at the World IMO, you sit in cars and watch movie clips. It's not set up for conversation, though - course our family always found that to be a nice change from trying to converse with each other for yet another meal. Relaxing, quiet, and always had good service.
Brown Derby - we were SO impressed with our meal here about a month ago for dinner. The food was so good, restaurant is beautiful. It's a more relaxing, upscale environment compared to the other two. We were there a good 2 hours and took our time. Food was delicious and service was good.
Good luck, hope that helps!