I play rotationally. I started with playing randomly any sims I was interested in, then I focused on about five main families and now I have merged those families into one big legacy family.
I have premade sims and other sims (that I don't play as actively as my legacy family) as background sims. It means they have some kind of stories and I may play them if I feel like it, but they are often just in the background and friends or lovers of my legacy sims.
My legacy family is in many different households, because I enjoy playing one, two or three sims at a time. Four is already a bit too much for me, because then I can't properly focus on all the sims and what they are doing.
Lately I have played focusing on aspirations and doing collections. I guess what keeps me engaged is the different situations my sims are in and the different things they do. Sometimes it is hard to choose who to play next, but I have noticed that at times it is important to just stick playing a family and then I start getting ideas what they could do next. Sometimes giving a makeover to the sim I'm playing is nice and refreshing.
I play on long lifespan, because I don't want my sims to age too fast, but I also want them to age at some point. I have noticed that long lifespan works the best for me. My sims have a lot of time to do what they want and if I want them to age up faster I can do that too.
I don't know if this was useful, but I hope you'll find a play style that suits you 💛