As far as "which dining plan" I do recommend the basic components of the Disney Dining Plan which offers 1 TS, 1 CS and 1 snack credit per person, per day. This is how we like to dine at Disney World regardless of whether we're on the dining plan. We have breakfast in our room (cereal, fruit or Pop Tarts from home), a CS lunch (usually just before we leave our morning park to return to to the resort for naps) and a TS dinner (a great chance to unwind and relax in the air conditioning and "recap" the events of the day).
My recommendation to decide if it's "right for you" is the most arduous one, but it's effective: make a list of the restaurants (TS) that you want to try -- 1 per "night" of your visit, and add up what you'd likely pay for a beverage/entree/dessert for the four of you at each one. (You can find all of the menus and pricing on this site.) Make a list of 2-3 representative CS restaurants you might visit and find an average meal price for the four of you for a CS lunch. Figure out the average cost of a "snack" per person per day (about $5-$6.75). Chart it out, totaling up what you'd pay out of pocket for 1 CS meal, 1 TS meal and 1 snack per person, per day. (Don't forget to calculate the kids' meals solely from kids' menus.) Then list the "price" per day for the dining plan, and see which total price comes out ahead (keeping in mind that if you do any 2-credit TS restaurants while on the dining plan, you'll also have to add in the cost of an extra meal, out-of-pocket.) This will give you an apples-to-apples comparison, although what you get on the dining plan might not reflect what you'd spend out of pocket if you were ordering as you please (maybe if you have your druthers you like an appetizer with your dinner, 2 snacks a day and no dessert...)
I did this for our upcoming trip (2 adults and 2 children). If I compare the cost of the DDP and the out-of-pocket cost for the same items at the same places, we just about break even as long as we're choosing only 1-credit TS restaurants with high price points. If I factor in any 2-credit meals, TS lunches or lower-priced TS restaurants, we're paying MORE with the dining plan than we'd pay out-of-pocket for the same items. More importantly, if I compare the cost of the DDP to the out-of-pocket cost of what we'd usually order at a restaurant (e.g., we don't typically order dessert with lunch and often not with dinner, I always order water instead of a fountain beverage, we sometimes prefer a hamburger to a steak, the kids sometimes split a single meal, I sometimes order an appetizer or salad instead of an entree), then we're paying at least 20% more WITH the dining plan than we'd pay out-of-pocket.
In my opinion, it's difficult to save any money using the dining plan. What you're really paying for is the convenience of prepayment. In the case of our upcoming trip, it's also serving the unique purpose of allowing us to tell a little white lie to one of our family members (that we're getting "free dining"), so that we can surreptitiously cover some of her costs.