I notice that Jane is from the UK. She may have no idea of the weather patterns in the states. Staying south of the Mason Dixon line would be recommended from December till mid/late spring. However, if one started in late summer/early fall and ended in December, that might be an interesting ride. Start in the northern half and conclude in the southern half. Being from the UK, I'm sure they get some pretty diverse weather year round. But, to respond to the original question of which direction to travel in December, definetly east to west while staying in the south along the I-10 corridor.
