Most likely to be open for Xmas time is SSR (but not THV) because it appears to be almost always available even for busy seasons even at 2 months out (at Easter time at 2 months out you could get anything you wanted at SSR other than THVs). OKW is also likely. AKV depends but you should have a good chance if seeking savanna view at Kidani. One issue is whether you must have the night of NYE because that is one that is likely to disappear before others.
You should try to reserve exactly 7 months out and here is what may be a significant issue this year:
Those attempting to reserve 7 months out at that time of year very often already have 11 month home resort reservations that they need to switch because the points from the one ressie are needed for the new one if they can get it. You cannot do that switch on-line and thus need to call to change. The risk for Christmas time is the on-line reservation system that went into operation in mid-January 2012, and its impact for Christmas time won't be known until this year at 7 months out since it did not exist last year. The on-line reservation system opens at 8 a.m. exactly 7 months out and the phones don't open until 9. For most kinds of rooms for most times of year, that probably won't have a major impact. For Christmas time, an extremely high demand time, there is a potential it could have an impact. Those making on-line reservations at 8 may well get the rooms still left open at AKV and any of the near-park resorts, leaving those calling at 9 to do a switch at a disadvantage.
As far as whether you should do Christmas time if you have never done so before, it is probably something to do once if, for no other reason, to verify your worst fears about huge crowds and make you appreciate practically any other time of year. What experiencing Christmas time can make you do is exclaim, "Wow, are the crowds light," when you go in mid-July. We have done Christmas several times but do so knowing that there are wall-to-wall crowds. In fact, on New Years Eve, you actually get situations where you literally cannot move on the streets at MK or World Showcase. And if your child has a birthday during Christmas week and you want Cinderella's Castle for that date, you had better be making that reservation at your first allowed opportunity to do so.