Hey Megan!
I'm so glad that you had a wonderful time! Disney World makes family vacations so easy and full of wonderful memories that it's easy to get hooked!
Last year I got to experience both the Halloween and Christmas party for the first time and they were both totally amazing, but being that y'all are newer to Disney World I recommend
Mickey's Very Merry Christmas Party.
The reason is that Disney World during the Holidays is pure magic! You know that feeling of anticipation and happiness you can see in a little kid's eyes when Christmas is getting close? That is exactly how Disney World feels to all ages in December! My family tries to go in the beginning of December every year now because we are hooked on that feeling and the weather is usually lovely.
At Mickey's Very Merry Christmas Party the Magic Kingdom is transformed into a wonderland, complete with Holiday music and SNOW as you walk down Main Street. There are stations set up where Cast Members give you hot chocolate and fresh baked cookies. The parade during the party is spectacular with gingerbread men, candy and toys dancing by. And when Cinderella's Castle lights up you can't help but gasp.
Seriously, even the Grinch and Scrooge would walk out of the Christmas party as changed men. It's worth it.
Whichever you choose, I hope you and your family have a Magical time!