Because I am such a huge WDW fan my in laws have suggested several times that we spend Christmas there. My answer is always

"ARE YOU OUT OF YOUR MIND????" Honestly I wouldn't be caught dead there the week before/of/right after Christmas. That is when attendance is at it's highest, lines are longer than you can imagine and the prices are sky high because it is "holiday" season. They even increase the prices for many of the meals. Sometimes the parks are so crowded they have had to close them due to capacity.
Spring Break is almost as bad. Again Disney raises prices during that time and you will find the parks to be very busy.
I would absolutely do the first week of Jan, right after New Year's. The prices drop drastically, you can usually find a good discount on top of that, and it will be much quieter. Weather can be iffy though, but even in March you may not want to swim or go to the water parks. It is most likely going to be long pants, short sleeved shirt and a sweatshirt weather. Cool in the morning, warmer in the afternoon, and cool at night. Of course this is all absolutely up to the whims of Mother Nature. We went the first week of Dec a few years ago and it was in the 90's all week-- even the locals were complaining of the heat. And I have been there in Feb when we needed winter coats, mittens and hats to stay warm.
I hate crowds. And I am cheap. I would always go with a time of lower attendance so that you don't end up spending most of your time in the parks standing in line, and you can get a lot more value for your money.