I did an in-depth analysis for our upcoming trip. We made our ADRs then I looked at the menues on allears.net and picked what we would order. It was cheaper to use TIW for us. However I didn't add the cost of the card into my analysis because we are definately getting it for an upcoming trip where we are staying off property. So it was not an additional expense for this trip. If you have to add in the price of the card, I think it will come out pretty close, but DDP will win out in your scenario.
Here is a link to my pre-trip report with how it worked out for us. I calculated the cost of what we would order normally (I drink water, we share one dessert) and what we would order with DDP (comes with drink, dessert for each person.)