Ron: If you are going in Dec., you MUST stay at WL. The decorations alone are worth the trip. Beyond that, the Lodge is simply wonderful. Sitting in the rockers by the fireplace is a great way to relax. Whispering Canyon is a terrific restaurant -- full of good food and good fun, too. The Lodge tours are great, the geyser is fun, the hidden Mickey hunt is wonderful. You are in the middle of Disney, but if you want to get away from it all, you can walk a few feet and find wonderful peace and quiet.
As others may have suggested, you might want to do a split trip: a few days at the Poly and a few days at WL. That way you can experience both! If you have a tough time choosing, this might be the way to go.
Whichever one you choose, I hope you have a truly magical vacation!