You'll be in for a pleasant change. These are great times of year to go temperature wise. I REALLY prefer WDW when it's a bit on the cooler side, much more comfortable. I lean toward December because of all of the holiday decorations and festivities and early in the month the crowds are still low. WDW doesn't get any more magical than it does around holiday time!
Being an experienced early Dec and early Feb visitor the weather can be quite fickle. We've experienced rain in Dec when a cold front came through. We went to MK on a Friday and I have to say it really felt like the holidays..it was nippy!! and dreary and drizzly, as yucky as that sounds it was fun buying a Minnie Santa hat to cover my "freezing" ears and then to get hot chocolate at the PLAZA in MK. That night we went to see the Osbournes and with the fake snow it really was perfect. (luckily we had some heavy outerwear). It only lasted a day, the next day it was sunny and in the low 70s.
February has been almost perfect. Both years we went not a drop of rain, 70s and sunny but still cool at night (40s and 50s), however our last day this past Feb. there were windchills in the 30s during the day!! I had my gloves and scarf and couldn't believe I was wearing them during the day! But, that was just the one day!