50's Prime Time is nothing special. The food was nothing to write home about, and the interactions got old after a while. At some point you would like to eat your food without being interrupted every 2 minutes.
Sci-Fi has good atmosphere and the food was better than Prime Time. I recommend going there.
I've heard mostly bad reviews about the Brown Derby and Hollywood & Vine.
I'm hoping to try Mama Melrose's on this next trip and I've heard both good and bad reviews. Maybe try a restaurant at a resort somewhere, there's plenty of good ones.