One of our favorite restaurants of all time is The Hollywood Brown Derby. It is fantastic, if you are on the dining plan it is 2 credits, but if you're not, it's not much more expensive than other places - if not on the dining plan I wouldn't order an appetizer or dessert anyway so it wouldn't be very expensive for the entree - plus they are big enough for sharing.
I haven't eaten at any other sit down restaurant in Studios, but we might try Sci-Fi on our next trip, the food just doesn't look very appealing anywhere but the Brown Derby to me...