I believe the second is less crowded, but we did the first last year because we didn’t want the kids to get tired and miss it. We staked out a great spot right in Frontierland and made friends with the girl handling crowd control. We told her we got our spot early(about 1 hour) so we could be front row and the kids could see well. People were trying to crown in and shove their kids in front of ours. She helped to keep anyone from pushing in font of us so DH didn’t have to start a fight. I would say get there early and find a spot. The headless horseman comes prior to the parade and you do not want to miss him.
They only thing I regret about MNSSHP is that we trick or treated. It really was a waist of time and the candy is not that great to warrant the time spent. Also, the crowds for trick or treating are more like mobs and the people act as if they have never seen a piece of candy. Picture a group of monkeys on a cupcake and you have it. Hit the parade, the unusual characters and the Haunted Mansion and you will love it.