I didn’t use mods in my games until relatively recently.
Sims 2: I don’t remember my first one.
Sims 3: NRAAS Overwatch and ErrorTrap. I think. I downloaded quite a few NRAAS mods very close together. I find the Anti Magic Scroll one useful, so that cookbooks etc don’t just disappear once you’ve finished with them.
Sims 4: MCCC, of course. I haven’t tweaked many of the settings. I allow Sims to continue aging during pregnancy (so if they have 10 days left as a YA at the start, they end their pregnancy on 7 days left rather than staying at 10), and I adjusted the maximum household size to 10, but that’s it. I’m also going to adjust the maximum number of club members to 10 in the future, but I’m not at the point in my story where I need it yet.
I don’t have many Sims 4 mods. Aside from MCCC I have one that allows plants to grow in every season, one that forces Sims to sit down at weddings, and one that adds character values interactions to the journal.