We opted to skip the parks that night, the crowds were just too much especially for our DD who was 7, we went to Fort Wilderness to the campfire and a movie.
I have been told MK is the worst as far as crowds go and Epcot is better since it is so much larger.
Take your patience hat, plan to arrive at the park you choose and spend the day, the parks frequently fill to capacity and they won't let you in.
As a Disney resort guests you are guaranteed admission to a park, it just may not be the park of your choosing.
I think people either love it or hate it - whatever you decide have fun!
We have done 2 NYE's and this trip we are checking in on the 1st while you all are sleeping!