If we're talking what LIFESTAGE that needs the most improvement, it's obviously babies. Why "obviously"? Well, for one, babies aren't even sims in TS4. They are objects that can be deleted and dragged around in build & buy mode like coffee tables or decorative plants. Babies needs to BECOME a lifestage because currently, they aren't. It's ridiculous that after 6 years, they still aren't sims. Babies aren't people according to TS4.
If we're talking existing life stages, I'd pick elders. Children also need a lot of improvement - they have nothing to do. They've had the same 4 aspirations to choose from since the LAUNCH OF THE GAME and are only allowed 1 trait, making children indistinguishable from each other.
My top 3 pick was:
1. Babies
2. Elders
3. Children
