It really depends on what you want.
Our favorite, by far, has always been the Prime Time Cafe for a combination of theme and food. We have eaten their three times over the years and have never had anything less than a wonderful experience. The wait staff is the hardest working, and most fun at WDW, IMHO.
Mama Melroses is fine, but is a straight forward Italian Restaurant and serves decent food in a nice atmosphere. It serves good food and costs a bit less if you choose wisely.
50's Sci-Fi is a gas for the theme! The food is just a pricey as the others, but is themed like what you would get at a Drive-In (Hot Dogs, Burgers, Fries....etc.) It FEELS like you are paying way more than you should. If that's ok, then it's great fun.
I think that they are all part of the current Fantasmic Packages.
We have never eaten at the Brown Derby, but have tried all the others.