Sims 4 traits that are actually worth picking

Gloomy is underrated if you play emotional sims, sad moods unlock some decent buffs. And Ambitious if you care about careers, they get promoted faster but get tense when they're not progressing. I'd avoid stacking three skill traits on every sim though, the household all ends up feeling the same.

Ones that actually change how you play, not just a moodlet now and then: Bookworm, Creative and Genius. Skills level faster and the matching moods come easy, which is a lot of the game on a legacy run. Cheerful makes keeping sims happy almost automatic. Kleptomaniac adds a whole interaction you otherwise don't get. Loner or Hates Children if you want a rough generation that plays very differently. Active is decent too if anyone is going for a fitness career.