To be honest, I don't really like any of them. But if I had to choose, I would choose Whispering Canyon for the food. I don't eat pork, but their pulled pork is really good.

(Still surprises me to this day that I liked it.)
Although the characters are great, especially Anastasia and Drizella and even Lady Tremaine at 1900 Park Fare, the food is not good. I may be biased since we try not to eat at any buffets. We absolutely do not like buffet food.
Sci Fi Dine In has a cool theme, but the food isn't good either. My children like it so we tend to go once in awhile.
The food at The Plaza isn't really great either and, as someone has already mentioned, it's a better place to eat for lunch. It's mostly sandwiches and salads.
Keep in mind that just because I do or do not like certain restaurants, it doesn't mean that you will feel the same way. I don't think you should avoid any of these places. But I just don't consider them a must do either.
Good Luck.