The weather is unpredictable for both the times you are considering. From April-October, you can count on it being HOT. November-March can be warm, pleasant and mild, rainy and warm, rainy and cold, or in some rare cases, dry and cold. There is no rhyme or reason, it's just Florida in the winter. We sometimes will be run our AC and Heat in the same week (just did that last week in fact). So you can count on both those times not being hot. But other than not hot, it's anyone's guess!
I have ride photos from EE taken exactly one year apart in mid December. One photo I am in a t-shirt. The next year I am wearing a coat, scarf, and gloves. But on that same trip where I had to bundle up most days, I did manage to go in the pool one day.
Bottom line is weather is nice at either time.
Crowds are going to be slightly less the week before Thanksgiving than before Christmas. If you are going after F&W ends and before the Thanksgiving crowds come, it's very nice and manageable. The week before Christmas won't be bad, but more crowded than week before Thanksgiving. Although it can depend on how the holiday falls. Basically, WDW will be slammed once most schools are out. If you can plan to leave the day most people start arriving, you're golden.
You will be able to see almost all the holiday decorations and events the week before Thanksgiving.
Enjoy the trip - it's my favorite time of year in Florida!