We have gone the week after Thanksgiving for several years now...prefer it to any other time....
The crowd levels are the lowest I have ever seen, the weather can be tricky....anywhere from cold to hot....we have had it where we have needed winter jackets during the day to shorts and t-shirts into the evening...but, only once or twice did we encounter any rain.
Everything is decorated for Christmas, the Candlelight Processional and Osborne lights are available...it is also a great time to attend MVVCP as crowds have not been too bad (although getting worse each year and we always go the Tuesday night after Thanksgiving).
My DH has decided that we wants to go during a warmer time so we can swim in the outdoor pools at night after we leave the parks so we have decided on October this year and I am not a happy camper..don't think he will be either when he realizes the crowd levels will be much higher and the heat will do us in (in October, we usually alredy have at least a foot of snow on the ground!)...
In my opinion, it is the very best time to go!!!