Neat sims have fun cleaning the house, I hate it when sims live in a mess so I always have one sim with this trait. Neurotic obviously has been said. To raise the bar quickly I also like the use of the hot tub, destresses and they can have fun. New favorite form of entertainment is the basketball court, and they gain athletic skill.
Obviously evil/mean spirited get a kick out of stealing candy from babies, and I think it increases their happiness bar