New Years twice here. Both were miserable. Millennium at Epcot and the following year at MK. MK made it impossible to even walk let alone ride anything.
We left the MK a half hour before New Year and stood outside the MK near the boat docks and watched the celebration in the sky from there.
It was wonderful.
I have been to WDW at every time of the year. Nothing was more crowded than NYE, because everyone seemed to be out and about unlike any other holiday celebrations where they are staggered.