What is the best deal depends on a number of factors. In your case more than likely the free dining is your best option.
Depending on number of nights at a Value resort free Dining is almost always the best, followed by gift card offer and room discount.
A number of factors determine the best deal. Room type, resort level, number of adults/children in the room, number of nights stayed.
At the moderate level it can go either way so is always best to check all 3. Usually it is free dining that is best.
At the deluxe or Villa resorts free dining is not always the best deal (depending on number of adult paying guests), the gift card is usually not the best deal either. Room discount is often the best deal (you can still add park tickets and dining credits). Exceptions can be Wilderness Lodge and Animal Kingdom Lodge as they are priced lower.
In every situation, I would suggest always trying all of the offers to make sure you are getting the best deal!!