The simple answer is how many days are you going in this trip and any other trips in the next 12 months. If the answer is that you are going to spend more than 8 days at the parks then an AP is the way to go from a financial point of view.
However, there is always the convenience point of view. Having used the length of stay passes last time I am now torn between them and an AP. I love having the water parks and Disneyquest available to me for "free".
We have always had AP's for the past 6 or 7 years because we like to have the flexibility of being able to go whereever we want, whenever we want, for however long we want. There is no need to be at the park from opening to closing in order "to get your money's worth". It allows you to go anywhere to eat because you don't have to worry about having park admission. If the fireworks are cancelled on the night you are using a day on your park hopper pass who cares. You can go back the next night just before fire works time and see them when you may have had a very relaxing day.
We have an eight year old and a two year old. I like to be able to change the schedule if necessary. (You know, meltdowns, temper tantrums, sleepiness etc.)
The negative point is the money up front for the passes. I know people who buy their passes a year ahead and then they don't have that expense when their trip bill comes in. Some people buy Canada Savings bonds through work and then buy them once they've accumulated enough money.
I like to tell people that my trip only cost a few thousand dollars because I didn't have to pay for park admission on my second trip in one year.
Decide whatever works for you.
