Arriving on the 26th you will get to see all the Christmas decorations and will not be dissapointed. Like a previous poster said the Christmas parade from the
MVMCP will be shown during Christmas week so you will not miss that. We went to WDW this past Christmas (from December 21st - January 2nd) and had a great time and it was nowhere near as bad as what people had made it out to be. Here are a few tips that I learned:
1) Make ADR's as soon as you can.
2) Make a day to day plan and a list of must do attractions for each day, but be aware you will not be able to do everything.
3) Do not go to the park with morning EMH, instead go to another park for opening. We did this and we walked on everything we wanted to for the first 2 hours.
4) Fast pass, Fast pass, Fast pass
5) Get out of the parks by lunch time, by then you will have done the rides you wanted to anyway and the crowds by then will be huge!! Take a break, have a swim, go shopping and then return later for fireworks, evening parade etc.
6) Take time to go and look at the decorations. We toured all the deluxe resorts to take photos.
7) View the Osborne lights during Fantasmic, it will be quieter then.
8) If there are 2 parades on in the evening, go to the later one, it will be quieter.
Thats all I can think of for now. I'll post more if I think of them!!