I give mine good traits most of the time, but this thread has got me thinking-- why is it that I hardly ever give them bad ones? I can't believe I've never even played a grumpy sim before!
I think the Goths have grumpy traits, if you wanted to experiment. Personally, I don't think grumpy is as bad (good? interesting?) as evil or mean spirited. Jared Frio always has tons of enemies in my games, because he's mean-spirited. Unless it's a townie that I play with, I never give Sims negative traits. I should though - it may make it interesting
I used to always make my Sims neat, but having a maid is more convenient, and when they're desperate to go to the loo and they can't because it's filthy, that's a bit annoying. Social butterfly (Showtime) is interesting, because they need a lot of social contact.
There are some that are really pointless, though, that I hardly ever use - vehicle enthusiast, for example, which I only use if I can't think of anything else. Or Loves the Heat/Cold (seasons) because I find that it takes a while for sims to be affected by the seasons.