Hi, Michelle! I think that the best time to go would depend on what types of things are going to be most important to your family!
My family prefers Mickey's Not So Scary Halloween party to Mickey's Very Merry Christmas Party. The kids love dressing up and trick or treating - it's like a bonus Halloween! We also really enjoy the EPCOT Food and Wine Festival. Even my youngest likes to wander around the countries and try the various items.
December will offer you not only Mickey's Very Merry Christmas Party, but EPCOT's holidays around the world and the beautiful Candlelight Processional, the Osbourne Lights at Disney's Hollywood Studios, and the opportunity to resort hop to see the amazing holiday decorations. It's really a magical time to be at Walt Disney World, especially if you can go earlier in the month and beat the holiday crowds.
November is very nice. The weather is usually ideal in terms of just the right amount of Florida sunshine but none of the humidity. If you avoid Jersey Week (which is the first week in November this year) and Thanksgiving, the crowds are generally light and you can expect shorter wait times than at other, peak times of the year.
Whenever you choose, you are going to find something wonderful going on! It's just a matter of preference.
I hope your vacation is magical, no matter when you go!