Which expansion pack should I get next?

I would recommend Island Living for the Occult player. I honestly wasn't that interested in it when it was announced but I got it for mainly the Mermaids and I find that I play with them all the time. I also really love the world and use it a lot, especially the volcano island. I put a shipwrecked pirate on the shipwreck lot using costumes from Spooky Stuff and Get Famous, a group of evil Sirens on the little island sand bar and made their Mer forms creepy and twisted, and I put a Voodoo Mambo in her rickety hut on the lot near the volcano (used the Realm of Magic pack so she's a Spellcaster). I'm putting a Mer kingdom in the western map of broken islands and deep water and I might change up the main section to be more of a "Tortuga, Smuggler's Cove" area.

Sulani has become one of my favorite worlds for its versatility for my gameplay style so I definitely recommend it. :)