What a difficult question to answer. There are many factors you need to consider. Do you have kids? Do you want an adult atmosphere or something more interactive and fun. What is your budget? Do you want all you can eat? Are you looking for characters?
We go WDW every year and, in my opinion, Brown Derby has the best food at DHS, but they are also by far the most expensive, and have a more upscale adult atmosphere. PT 50's, Sci-Fi and Mama Melrose all cost about the same. Hollywood and Vine offers the best value for your buck (considering vareity and it's all you can eat). They also have characters which can be a lot of fun.
PT 50's has very good food and a very fun environment (make sure you wash your hands and note the type and color of soap). The pot roast, chicken pot pie and chicken are all EXCELLENT.
Sci-Fi is cool because you get to eat in a drive-in type of atmosphere and see clips of B rated movies. Some are so dumb you have to laugh. Their ribs are very good as are burgers and shakes.
Mama Melrose has some decent Italian dishes, and is similar to Brown Derby in that it's more of an adult atmosphere.
Our personal favorite is PT 50's, but it really depends on what you want considering the factors I mentioned earlier. Bottom line....something may be better than something else, but you aren't going to go wrong no matter what you choose.
Hope this help you somewhat.