Hi Gloria! Unfortunately, both dates you provided will be quite busy! In past years New Years Eve will have the largest crowds and a day that is very hard to get into the parks. I would probably opt for the earlier time for that reason alone.
Christmas at Walt Disney World is unbelievable and the decorations and entertainment will have you in the holiday spirit in no time. Keep checking the web site,
www.disneyworld.com, for the schedule for the special parades, Mickey's Very Merry Christmas Party, Candlelight Procession, and tours as you will want to make reservations for many of these. Since this is a very busy time please also make sure you have dining reservations in place and these can be made 90 days prior to your arrival. (407-939-3463)
If you choose to be there on Christmas day remember the Disney florist can provide you with a small holiday tree for your resort room as well.
www.disneyflorist.com Magical things can truly happen for you during that time to make your stay memorable!