My DW and I have been several times this year from peak times to less crowded times, and we have basically decided that nobody knows what they're talking about as far as crowds go. MK was most crowded on Saturday for our first trip, and Monday on our last trip. There really doesn't seem to be a lot of rhyme or reason to anybody's list, and depending on who you ask, you will find different people say to go to different parks on different days. Some lists make their judgments to keep you away from EMH, but I suggest making use of EMH to beat the crowds, and then leaving for another park. I would just go with my gut feeling.
Are you staying on property? We found that the best strategy for avoiding crowds as much as possible was to get up early and be at the park for EMH or at park opening if there were no EMH. Late morning, you'll start getting hot and it will get really crowded. This is a good time to have your advance reservations for lunch. Then go back to your hotel and take a nap or swim. About three or four, get up and go back to one of the parks. (If you have PH tickets, it's a lot more fun to go to more than one park a day). You'll have a couple of hours of crowds once you get back, so you can have an early dinner to avoid them. Or, once you've already seen Wishes, Fantasmic, and IllumiNations, these are great opportunities to get into restaurants that are usually crowded. Also, you can generally ride as many rides as you want while these shows are going on without much wait. NO MATTER WHAT--go to Magic Kingdom's Evening EMH. This was the best time we had on our trip, and we got special opportunities not offered to the general public or at other EMH.
We found that following these general rules helped a lot more than trying to go to a certain park on a certain day to avoid crowds.