I try to avoid Mean-Spirited, Dislikes Children, Losers, and Grumpy (maybe slobs too) for legacies. I want partners of about the same age, and skin color doesn't matter at all, but also because as time goes by, the town blends all shades and turns most sims cafe au lait color anyway. I do avoid hideously ugly sims for legacies, but have enjoyed playing them for fun.
As with real people, I like smart, interesting, fun, talented sims, and Family Oriented is great for legacies.