Fall, winter and early spring in that order. Depends on what you would like best. Halloween , Christmas , St Patty's or Easter decorations and special parties in the MK.
My two favorite times are: Thanksgiving-Christmas cause' everyone decorates there sites and their are special events at the parks and all the resorts and parks are holiday decorated too.
And
Late winter/early spring cause' cause it's not the current 90 degrees with high humidity like it is right now. The a/c doesn't have to work so hard and I don't get all glisteny just sitting outside or walking the kids.
This is my thought too. We have been there various times throughout the year. Best time was had when we were there for longer than just weekend as we were able to relax versus trying to do it all, KWIM.
May for us. It's not hurricane season (actually it's the dry season so it rarely storms during the day). Weather is still cool enough and crowds are very, very low.
We have been as a family in Oct. and Jan. As I kid I went in the summer. By far the best time to go in my opinion would be LATE October near Halloween. It is still pretty warm but the MNSSHP makes up for that! That party and the whole week were the best time we have ever had at WDW. The campground decorations are AMAZING and the MK is beyond words. They really go all out for the party and my kids will NEVER forget it! We had a GG with my parents, sister, hubbie and baby and my hubbie and 2 kids. Everyone dressed up and got 3-4 pounds of candy each. It was so fun to see the characters in costumes and have them all to ourselves. The parade was the best we have ever seen at Disney and the FW were unlike any they have any other time.
January is really great for lower crowds and really cool temps. You have to bundle up and take off layers and I hate to be cold. The only time we about froze was on the ferry boats at night and early morning. You need a lined jacket, sock hat and gloves for most days and then again you might only need a tee and shorts on others. Too much guess work...go in October! You will love it!