Id' have to say either of the two last weekends of the month should be good. We'll be going this year from Jan. 12th - 23rd. Had to bump it up so the kids won't miss as much school but now we have to deal with MLK weekend crowds. Hopefully it won't be too bad. On secound thought it doesn't matter were still going to be at WDW. Maine
My main recommendation would be stay away from New Years Eve weekend (12/31-1/1) and MLK Weekend (1/14-1/16). If you are staying away from the marathon and cheerleaders, I think that leaves the last two weekends.
Personally, I will be there 1/21 - 1/27 and I can't wait