Savant is my must have for all my Sims.
Artsy ones also get Creative Visionary for sure.
Since I'm playing with extreme weather effects, everyone needs basic acclimation to heat and cold too.
Those Sims who need to be out of home for a long time (like DJ or archeologist) also get slower needs decay.
However I never buy those last four traits that fully stop the needs decay even when I have a lot of spare points - it's just too unrealistic :)
Everything else depends on the character/personality/careers etc.
My Sims have around 20-30 traits (including aspirations rewards).
