My family vacationed over Christmas at WL in 2004 & at POR in 2005, both times for 10 nights, and POR between Christmas - New Years in 2006, and POR mid December in 2007.
I'm glad we stayed at WL over Christmas once, but it wouldn't be my first choice again. This isn't what you wanted to hear, but I would choose POR over WL again for a December vacation for a few reasons:
1. Price
Depending on what type of tickets you choose POR room + tickets for the family could cost the same as WL room only. Rooms and amenities are slightly nicer at WL but not not so much nicer that I
must stay there
2. Food Court
The food court at POR is much better than Roaring Forks IMHO for breakfast, lunch, snacks, etc. Dinner most likely would be at another resort or a park (I couldn't eat at AP or WCC every night!). If we want 'room service' at POR one of us goes and brings back a tray
3. Crowds
POR handles the crowds better and doesn't feel as crowded. MHO!
The 10 nights & days we stayed at WL there was never an empty seat in the lobby, it was packed with visitors! In contrast, I spent lots of time in the POR lounge enjoying the decorations, fireplace and entertainment.
4. Atmosphere
It just feels relaxing! And Christmas decorations are beautiful at POR, more subtle than WL, but there are many all around the main building.
5. Room view is not as important.
I'd be happy with just about any room view at POR but only want a main building courtyard view at WL
Some downsides to POR:
No balcony. (not important to me anymore)
Only 1 hot tub!
The deocrations are beautiful, but if your room isn't located near the lobby you may have to make a point to walk thru and enjoy them. I enjoy a leisurely walk to/from my room - but would feel different if I had small children and strollers
It can be a hike to the main bld from some rooms.
Santa visits on Christmas eve, but characters don't. WL had Santa and characters
Boats & Buses:
WL has a boat to MK and POR has a boat to DD. Everywhere else is buses from both. I can't really complain about the bus service, in general, for either resort in the times I've been at them.
Good luck whatever you decide!