I'm an AP and this past year and I have been to Disney many times (with a 2 year old) including on 4th of July, Christmas Eve, December 30th, and this past Tuesday (Spring Break) and I can tell you the two worst days I've had as far as crowds and a feeling of "OMG GET ME OUT OF HERE!" was December 30th, and this past Tuesday (both at MK.)
On 4th of July we got there at rope drop (8am) and left around 1pm. I was able to make reservations for The Plaza a few days before. We were able to do several rides and meet several characters (including Mickey, and Princesses). We had a very pleasurable morning and a sit down lunch (even feeling at first like 'where is everybody?") After lunch we decided to go home, and when we left is when we saw the people parked on the grass and found out the park had been closed to capacity. But it never felt insane. (Granted, I didn't stay for fireworks, but we still had a great day in the park.)
Christmas Eve was magical. It was crowded, but not insane. We saw ETWB, Mickey, all Princesses in PFTH, rode Small World and Carrousel and then ate lunch and saw the Christmas Parade. Again, crowded, but not insane or smothering. A very happy day at MK. Left around 4pm.
This past Tuesday we got to MK around 1 and left at 5 and I wanted to shoot myself for ever entering the gates. We had three FP+ (Rapunzel, Little Mermaid Ride and POTC.) Well I posted pics of the POTC return line (we didn't use our FP+ and left the park.) The mermaid area was a clustered zoo, only Rapunzel did we get in and out of quickly, but the meet and greet felt a bit like a 'kiss and kick you out of the door.' (which we NEVER feel like we get when meeting them- but they no doubt knew about the zoo outside waiting to see them.) Small World had a wait of an hour, and I just had to tell my daughter no. The lines for drinks looked to be 3 miles long and you could not manuever from point A to point B without feeling like livestock. (and this is what the week between Christmas and New Year's is like as well.) UGH!!!!! NEVER AGAIN!