I have spent hours wrestling with this.
Our family is me, DH, and DS14. DS is tiny. He eats very little and hardly ever finishes a child's portion.
We looked at the counter service dining plan. The ONLY way to come out ahead on that is to ALWAYS spend a minimum of $12 on CS meals and ALWAYS use snack credits at the max value of $4 each. OK, not for us.
Basic DDP. We like appetizers, and we like signature dining. By the time we factor in tips, appetizers, and needing double credits for dinners it is such a huge inconvenience it's not worth it.
Deluxe DDP. We had this for about a week of our 2008 trip. OMG! We lost SOOOO much money! Back then the plan was $70 per person, per day. So $210 per day, plus tips. We were spending at least $60 per day to tip on a buffet breakfast and a signature dinner. I realized there is NO WAY we would spend $270 per day on food with the TIW card. Heck, there is no way we would spend that much on food WITHOUT the TIW card! It was INSANE!
Our upcoming trip is split 2 nights in a regular room, 13 nights in a villa. I tried up, down, and backwards to get ANY of the dining plans to make sense for us and I couldn't do it.