I use both good and negative traits on my Sims. Sometimes both on a single sim. Like I love the Hot-Headed trait for example. Although, honestly? It's because the male characters on TV shows and movies I seem to be most attracted to are stubborn, hot-headed guys. So it's kind of my "type" in a way.
I almost always use mean, snob, and materialistic for one of my OCs who I recreated on Sims. (and then cheat ambitious on there) Basically, she's your typical mean girl. Just more determined and ambitious.
And I've only recently started using evil and non-committal. Which are again, for story-telling purposes. Recently, I've created an evil vampire who I later plan on reforming (through the use of the Vampire with a Soul) mod and he inspired a new paranormal-romance book series for me.
I do tend to stay away from the kleptomaniac, erratic and slob traits though. I don't know why, they just don't appeal to me.