The pizza's (flatbreads) at Mama Melrose's (Table service) are really good.
50's prime time is a fun restaraunt with comfort foods.
Sci-fi is also fun with sandwiches and milkshakes and other good food. Check out the different menus at www. wdwig.com
Mind you we have not been in many years, but we used to go there all the time. I can picture so clearly. It is really great table service(upscale-ish) but not too formal. It is old Hollywood. I would also recommend the Cobb Salad. I am counting the days until I can enjoy it there(10 and counting).
Adding my vote for the Hollywood Brown Derby... Although it can get a bit noisy at peak times, it's still the best restaurant at Disney MGM to have a great meal and enjoy the ambiance of the restaurant.
We ate at 50's PTC for the first time this past June and loved it!! DD10 ordered the meatloaf and ate all of it. DD3's main diet consists of chicken, fries and ketchup so she was very satisfied here too.
If you're going with kids, I'd recommend the Sci Fi Diner for its really fun atmosphere. It's dark inside, because of the movie theater theme, so a nice break for lunch.