I think where you have children who are considered adults for the dining plan (as we do) you're better off with the TiW. I just can't see my kids getting our money's worth on the DP.
Only if you avoid the buffet restaurants or the "pay one price" places. If you prefer those places the DDP could be better because you are stuck with the adult prices no matter what.
I think there are so many factors and variables that it is impossible to say one is better or more convenient than the other in general terms.
Questions I would ask myself when deciding:
What are the eating habits of me and my party?
Do I prefer sit down restuarants?
Do I qualify to purchase the TIW Card or will there be an additional cost to qualify (i.e. if you don't already live in Florida or you are not an AP holder, there will be the additional cost of getting an AP versus a MYW ticket).
How many meals per day do I plan on eating and how regular are my eating habits (ie do I eat at 5pm everyday or get grumpy?)
Do I want to drink wine or cocktails with my sit down meals?
Do I go into a restaurant and automatically order an entree or do I look at the menu and order whatever looks good (2 appetizers, or a soup and side salad combo, split entrees with another person).
Do I generally eat dessert on vacation?
How likey am I (or a member of my party) to order steak dinners? (to me if the answer is "very likely" go with the DDP).
How cheap am I? Is price my first consideration when ordering?