I use a bunch but there are three I probably just wouldn’t even play without.
MCCC for all the reasons others have said.
And then Wonderful Whims for its attraction system, combined with The Chemistry System by thepancake1. With these two together, I imagine that the chemistry system is like emotional/friendship chemistry since it applies to all Sims including family members and children. Then the WW attraction system has to do with romantic attraction. With these two enabled together, it makes looking for a partner so much harder and more fun. My sim might see someone they think is the hottest ever but once they start interacting they have terrible interpersonal chemistry. I won’t keep two Sims together long term unless there is a decent amount of both attraction and chemistry.