we like both for different reasons....
sci-fi is cool, dark, quiet & you get to watch movie trailers
the food is eh - burgers, fries, shakes - can't go wrong with the basics
50s prime time is bright, colorful, noisy & you get to watch those B&W TVs
the food is better - homestyle, "comfort" style - pot roast, fried chicken
we always go to both every trip, on the same day (sci-fi at 1130, 50s at 4)