Beth,
Two years ago we went during MLK weekend. It was wonderful. There were hardly any lines, the weather was very nice all but a day that it was raining and then it was a little cool (but the parks were completely uncrowded that morning). The kids could swim in the hotel pool although it was a little too cool for us (but we like water very warm). We just got back last week as we decided to try in October because the kids really wanted to go to Blizzard Beach. We had a wonderful time, but I wouldn't go back in October. They had a record high the whole time (91 - 95) and it was so much move crowded than in January. I will definitely be planning my next trip in January and probably during MLK.