All of my worlds have a purpose in my game, but the ones I play in the most are the ones that are designated as part of The Myst, the magic world. Those include Glimmerbrook, HoB, Sulani, Granite Falls, Mooncrest (created by merging Newcrest and Magnolia Promenade), plus Copperdale and Britechester for schools. San Myshuno is a sanctuary city, and gets a lot of play. Moonwood Mill is an ally. Forgotten Hollow is its own thing. All the rest are human worlds, with Windenburg and Selvadorada being Myst adjacent, thus having some connections and magical aspects. Windenburg gets a lot of play because that’s where I’ve placed The Blue Moon Tavern. Oasis Springs and Strangerville harbor aliens.
I use the All Worlds Are Residential mod to bring Granite Falls and Selvadorada into my game as something more than vacation destinations.