Do both, they are worth it. For Epcot I suggest watching Illuminations near Canada, then head to Soarin right after. Once you get off, I usually ride Nemo to allow crowds to dissipate, then hit Test Track via single rider line. Finally head to Norway and you should be able to ride Frozen at least twice sometimes three times.
At MK just stay away from Tomorrowland (everyone goes there) and hit up the left side of the park for the first hour, during the second hour every ride in Fantasyland save Peter Pan and Seven Dwarfs will be walk one, do the rides you want and pick one of the two to do at the end of the night.