NB: there appear to be some MASSIVE misconceptions going around as to what I'm actually saying here, so I'm going to clarify as part of this edit inside the various sections. But first, some theory.
Surviving ANY end of world event, whether it be the end of power generation or the zombie apocalypse comes down to one factor - preparation. If you're not prepared for the end of the world, you're highly unlikely to survive, but the longer you survive, the better your chances of remaining alive. Remember Y2k? We all had our pantries stocked, fuel in the car, just in case. Same deal here.
Also, I'm not suggesting that this is a great time to survive; not at all. Most people are still going to die. What I AM saying is that because people are already planning to have family around them for an extended period, and have stocked up on food, blankets et al accordingly, they have a better chance of survival than they otherwise would, but in many cases this is still not going to be enough. But, on with the answer...
If we narrow it down to North America in particular, there are several advantages to this being your chosen date.
Christmas is often seen as a time of family, so small family gatherings are happening all over. This is actually a good thing, because less people are going to be out trying to find loved ones, and those you care about are already grouped together in a small 'clan' that is determined to look after each other.
These aforementioned families have already stocked up for the Christmas period and therefore have an advantage in terms of managing food supplies going forward in the initial chaos while they work out what to do next to sustain themselves.
To address comments; I'm not suggesting this is a long term fix, merely that this will give you enough time to plan your next move. The fact that you've planned for a feast means that you can ration it out for a bit and figure out how to get to a ready food supply from there. If you have this, you have a small buffer. If the end of the world occurs without this buffer, then the very next morning you're raiding the local supermarket like everyone else. That lowers your chances of survival, especially if people start bringing guns to this particular party.
Sure, not nice to be out in, but if the power goes out, all that aforementioned food hoarded by the aforementioned families will go off at a slower rate. Still not good if you're in (say) California, but in Illinois or New York, you could almost freeze your food by leaving it outside.
To address comments; I'm not suggesting here that this will freeze food, and in point of fact that would be counter productive. What I'm saying is that if you somehow find a way to get your homes warm, you don't want your food in there because your fridge won't work. Put your food in an eski (or cooler for our US friends), out on the snow, to keep it cold, not frozen. You still want ready access to that food in the short term.
Because the families are already together, there's little need to travel meaning that the roads are freer for the emergency services, assuming of course they can get their cars and trucks working. That means that as issues arise, the emergency teams can respond more rapidly than they could if everyone was trying to get to family or just plain get out of dodge in a disorderly fashion.
This is still a catastrophic scenario by most standards. Large population centres (cities) consume a lot of food, and produce almost none. Many of the people in these population centres start dying after a few days no matter what you do and civil disturbance will be on an exponential curve when the food starts running out. Add to that the fact that the cold is a two edged sword insofar as our warm-blooded metabolisms mean that we need to eat more during the cold than otherwise, so that food that lasts longer before spoiling gets eaten faster to avoid starvation.
Also, EMPs and other technology neutralising phenomena will make it much harder to coordinate responses and the like, and most of the people who survive from the cities will do so by walking out of them immediately. Some of those families (for the reasons mentioned above) will be less likely to do that at Christmas.
The real winners out of a doomsday scenario at Christmas in North America are going to be the small communities across the food belt of the USA, where they have family around them, a supply of food and the capacity to grow more as they go, not to mention having herds of cows and sheep to survive off while crops regrow.
To address comments; I can't speak for Iowa as I've never been there, but ultimately when we talk about the theory of survival, it comes down to this. In the short term, having family and friends close and ready to work together as a team, as well as reserves of essentials like food and blankets, increases the chances of your survival, but doesn't guarantee it. In the long term, being where you can grow and store food increases your chances of survival, doesn't guarantee it.
Just like being caught outside without heating in the snow belt is going to massively increase the risk of you freezing, being in the Arizona Desert with no air conditioning, food or water is also going to decrease your odds of survival.
Ultimately, you want a place where it can be temperate most of the year and have a steady supply of food, for long term survival. But, you don't need to worry about long term survival if you can't survive in the short term. So, being prepared by having your family close and a stock of food is your best bet. That sounds like Christmas, to me at least.