OK, we do all of the above... In the last 3 years we have done Spring Break (not Easter), days before NYE but after Christmas Day and days after NYE.
I really do wonder how many of the negative comments come from people who have experienced these times and have first hand knowledge of what it is like. And pictures can be very deceiving because if you take a snapshot in time of Main Street mid-day or after fireworks of course it is going to look ridiculously crowded. Here is my take having recent experience with all of the mentioned times.
1) Most crowded will be week after Christmas through NYE. Only experienced one stage 2 closure during 3 visits. Nothing to worry about as you are on property. New Years' Day is not crowded by the way...
2) Least crowded and least enjoyable (heat and humidity) is Spring Break
Managing the crowds is the key for us. We never get in a stand by line of over 20 minutes. We always get 8-10 FP+ reservations per day and many more usually at MK. Use the
MDE app to your advantage.
We have not found significant differences in wait times and dining times for ADRs. We have one per day, usually dinner. We now use mobile ordering for quick service so no standing in line for that either.
Our plans are of two types:
1) Morning EMH a park, FP+ rides 10-1:00, leave park for our resort or to see Christmas decor at other resorts, park hop for evening dinner continuing to use the app for rolling FPs.
2) Arrive in time for 1st FP, usually about 10:00, modify and ride as many as we can until park gets crowded (maybe 2:00), return to resort or resort hop, hit evening park with ADR and late EMH.
Generally speaking we usually leave the parks during the crowded times and try to make use of rope drop and EMH. We also stay at Wilderness Lodge and many nights will cap off the evening there before taking the short boat ride back to the hotel. You can get a lot done at MK while everyone else is waiting for and then enjoying Happily Ever After.
We have done NYE at all three parks. Epcot handles crowds best but don't even try to leave any of the parks immediately after the show. Wait an hour or more unless you can walk to your resort! Getting on the buses and monorail can be insane! Boats are a bit easier. We only do NYE at MK with a fireworks dessert party. You can see MK NYE fireworks on the 30th as well. They are amazing while riding BTMRR by the way! So this year we plan to do MK fireworks on the 30th and stick around for EMH and Epcot on the 31st with a late evening ADR. We do not nor do we find it necessary to camp out for hours holding a spot at Epcot...it just is not needed. It is a beautiful time at Disney and this year the crowds should be less as marathon weekend is the following week, unlike last couple years.