The best times to go to Disney are typically the times when others aren't willing (or able) to go. It seems that the beginning of September is an excellent time to go. (Not that I have been there at that time). The reason is because most schools are just starting back up, and most parents aren't willing to take their kids out of school for an extended vacation just after starting a new school year. So if you don't have school age kids, that could be a good time.
I can also tell you that we like to go during Thanksgiving (Checking in on Thanksgiving Day after driving with our camper from NE Pennsylvania). The rest of that week and the weekend tend to be pretty crowded, but once Monday comes, it's much better. Still a fair amount of crowd but manageable.
Weekends are almost always going to be busier than weekdays, particularly if there is a "Holiday" associated with the weekend. Keep in mind holidays other than US holidays. People always try to maximize their vacation by extending a holiday weekend for their vacation. That's actually what we do with Thanksgiving (mostly so the kids don't miss too much school). For us the kids have a half day on Wednesday before Thanksgiving, and are off until the following Tuesday when they return. (Here, the first day of Buck Hunting season starts the Monday after Thanksgiving, and many schools just give it off because historically so many have just taken it off anyway). So we leave Tuesday (before Thanksgiving) after work for arriving on Thanksgiving morning. Then we stay the rest of that week and of the next week. We then head back home that Friday or Saturday. That way we have enough time to enjoy what we want and plan events around the crowds,
