I have four saves that I use, depending on what strikes my fancy at the moment.
Legacy/Family Style: The goal is to keep the family line going as long as possible. This tends to be my most "normal" game in which Sims typically have traditional careers and as adults, have one or two kids. Normally I keep them in the more low-key worlds, like Willow Creek, Newcrest, and Henford-on-Bagley. Those worlds are slowly being built with lots of homes good to raise families, and I try to protect the townies/premades that have large families. I'm on the eighth generation right now, which is a teenaged girl and her elderly father (and a big floofy white dog). They were living in Henford-on-Bagley but needed a change of scenery, so as of yesterday they are temporarily in Sulani as the first family I've ever played that's gone off-the-grid.
Fame & Fortune Save: This is where I try to keep everybody in the household with high celebrity levels and spend a lot of time out-and-about on community lots. I tend to stay in the glitzier, city-ish neighborhoods, like San Myshuno and Del Sol Valley so that my Sims can run across townies/premades with their own fame levels. For a while I was just playing with one young guy who wrote songs and hung out at the karaoke bars. But since I don't have any children in my family save right now, I ended up giving him three toddlers. Each toddler has one star of celebrity level (which they got when they were born). I'm trying to get their celebrity levels higher. I do not know if it is possible. Anyway they are keeping their father very busy.
Occults Save: I'm still collecting packs, but eventually this will be full of supernaturals and other Sims that are colorful/weird/stuck with traits that could be considered negative. Forgotten Hollow isn't particularly inspiring to me, so I ended up plunking down some Victorian homes in Magnolia Promenade, of all places. I currently have a household of three young adult roommates, which include a vampire pirate that likes to paint, a childish Actor that dresses like one of Robin Hood's men, and an erratic video game programmer that I'll eventually turn into a mermaid.
Miscellaneous Save: I don't really worry about anything in here. Sometimes I'll use it just for building. Sometimes I use it to test new packs. If I feel like playing a certain kind of Sim, I'll sometimes pop them in here and play them for a few days. Right now I think the active household is a lady with a bunch of cats.
I stay with one household per save, but if I get bored of them, then I just throw them into another house and start a new household in the same save. I tend to be pretty loose with my rules. It is really just about keeping me entertained!