I always try to go in early December. Especially on weekdays, the crowds will be low. Weekends they still get fairly busy (not like spring break busy, but not 15 minute waits either). I'd say they're consistently low whereas February & January are a little more hit & miss these days. Plus, December at Disney is just wonderful. The Christmas spirit at Disney really makes me FEEL like it's Christmastime. One of my favorite things to do is a monorail trip over to GF, get some mulled wine, and sit & listen to the orchestra playing Christmas music. I'm not a fan of eating the gingerbread but going around to see the houses is super fun too.