I avoid any trait that makes my sim in a bad mood for no reason, like hot-headed (just because), hates children (they are always around), evil/mean, insider (rarely play clubs), vegetarian (i always forget to check my food) and so on.
But funny enough - I love romantic, family oriented, foodie, active (they hardly gain weight), materialistic and snob which some of you hate.
But most of the time I give them traits that makes everything easier like cheerful, neat and kind.