My most fav trait was only in Sims 3 - the Proper trait. I was so happy to have that trait and really miss it.
I also like the Sims 3 version of the loner trait - it is spot on compared to other versions of that trait we had. But the most fun trait I ever had has to be the Coward trait. Caused me to go in fits of giggles more times than I could count in Sims 3. My most played traits seem to be loves outdoors, genius, and friendly.
I do not like any of the mean traits or evil traits - as I do not enjoy seeing deviate behaviors in my game from my own sims (oddly I don't mind having others sims in my game that do have those traits if they are Vamps anyway, I just don't play them but do not mind interacting with them) - that said though I do think the Sims 4 sims are a bit too smiley and happy acting for my comfort level most of the time. I also never give any sims the traits of hating kids or animals or being mean to anyone. I suppose I enjoy my Lala Land but truthfully wish they were a little more normal acting. I mean Sims really should get and act angry to a sim that makes them mad - not smile and keep befriending that Sim. Maybe walk away in a huff - let that sim know you've made them angry. That I would find normal in even the nicest sim. So I could see some adjustments in behaviors of the sims of all traits.