I heard great things about the week before Thanskgiving. (I would try to avoid the whole week of Thanksgiving though, including the weekend before it!)
Overall, almost every weekend, including Friday nights, has been very crowded at
Disneyland lately. Three years from now, that MIGHT be a bit different (one plausible prediction are that there will be fewer AP-holders a year from now than there are now, which may mean fewer people coming to Disneyland for a few hours after work/etc.).
Weekdays when kids are in school are much less crowded. The park was magically un-crowded this year on Wednesday - Friday morning in the second week of December (12/9 - 12/11). Weekends were predicted to be awful, but Friday evening it was drizzling so it wasn't bad as far as crowds. Saturday it was cold and raining pretty much all day so it wasn't bad for crowds either. I don't know about Sunday; the weather was wonderful but we left about 2 PM so the park hadn't gotten too busy.
We were VERY lucky because we went on days right after the cast member parties (when the park closes early). A DISer theorized (I think correctly) that offering Fantasmic and keeping Disneyland open until 11 PM on Wednesday and Thursday were a way of compensating for the park closing early on Monday and Tuesday, rather than a prediction of large crowds on Wednesday and Thursday (the crowds were very light).
As I understand it, there were weekdays AFTER ours that Fantasmic did NOT run--and if it would've only run on weekends during our trip, we may not have managed to see it

, since it only ran one show out of 4 on the Friday and Saturday night we were there.
I believe the week after we went started to pick up as kids started going on winter/Christmas break, but I think weekdays were still probably fine. I understand that last weekend was extremely busy.
The Electrical Parade wasn't running during our trip, so that is definitely something to consider. That said, I'm not sure what will be going on three years from now--the parade may not be seasonal for just the busiest times of Christmas, or alternately it might not be running for Christmas at all!
Anyway, assuming things are the same 3 years from now as they are now, I think I would personally go earlier to avoid crowds (some schools end the semester by the end of the second week of December), rather than later to see the Electrical Parade. Obviously different people have different priorities, though. For me, if it were likely that Fantasmic would only be running later in the season, then I'd strongly consider going later versus earlier, but I wouldn't personally brave bigger crowds for the Electrical Parade. If that parade is important to you and/or your family, then that's the choice you can make.
I hope you enjoy planning! (I know I always do.

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