I have Sims living in all worlds in the game, but I prefer the worlds that came with the expansions, instead of the base game ones.
I recently bought Snowy Escape on sale, and the world that came with it is currently my favorite world.
Sulani is actually one of my favorites, because I like the look of it. I also really like the worlds from Get together and City living as well. I like Strangeville as well.
I really like the worlds from Vampires and Realm of Magic, but they feel kind of empty overall, and I wished they would've done more with it. In order to live in RoM oyu have to move into the library section, and you only get one house really in Vampires. I still like both worlds, though.