Hi Ruth! How lucky you are to be spending ten days at Walt Disney World in December! If you wanted to eat a table-service meal on most days of your vacation or you wanted to dine at several signature restaurants, it would probably be worthwhile for you to upgrade to the regular
Disney Dining Plan, which includes one Quick-Service meal, one Table-Service meal and one snack for each night of your stay. However, since it sounds like you're just planning to dine at just a few sit-down restaurants during your visit, you'd be better off financially to stick with the Quick Service plan and just pay out of pocket for the Table Service meals.
Technically you're supposed to only use Table Service credits for meals at the sit-down restaurants and not at the counter-service restaurants. (Some guests do report, however, being allowed to use a Table Service credit for a Quick Service meal, but I wouldn't count on being able to do that, and it's really not an efficient use of your money.)
Come visit us again at the Moms Panel if you have more questions! We'd love to help!