Any more than 4 and it becomes a bit of a chore. In large households I find myself just caring for needs rather than building skills or storytelling, the latter being where I derive most of my fun. There's just no time. Everyone is so needy!
I also like it when my sims have a bit of a social life and that is nearly impossible with a lot of sims. I don't feel as invested in having them make friends when their needs are down. Really, the moment they are out of work or school it's "Okay who's hungry?" "So-and-so needs a nap... And a bath. " "You want some fun? Sorry, the toilet needs to be repaired first."
