The Plaza is sandwiches, burgers and ice cream and one of the least expensive table service restaurants in DW.
Garden Grill which is a character meal is an all you care to eat family style dinner with a fixed price per person so much more expensive than The Plaza.
You can look at the menus on the Disney dining page or allears or wdwinfo and if both appeal, I would choose the restaurant that is in the park you'll be visiting that day.