Lifespan

It really depends on my save that I'm playing, but typically I keep it on normal. If I'm rotating a few families and play with aging on long, too many of my sims develop all of the traits and skills and every one is too samey. It's boring for me if all my sims have all of the perks and I like them to be different and have different things based on their lifestyles or interests. If I'm only focusing on just one particular sim or family though, then I'll set it longer and let them complete more.

I have aging set to only active household though. Without story progression, I don't like sims to just die off before they can have a relationship, family, career etc. The only time I turn aging on for the whole world is if I'm doing the 100 baby challenge because my matriarchs need donors to keep spawning. :D