Which pack should I get next?

It really depends. JA has some great CAS and Build Mode items, but Selvadorada itself isn't a good vacation destination. The temple stuff is really fun, but it's something you'll only do every once in a while, with the right sim.

Vampires is great, though. They're super fun and in-depth without being intrusive. The Build Mode is good for rich, creepy or haunted houses, but also makes for good Halloween decorations. Forgotten Hollow is also a nice and atmospheric neighborhood, though it's very small.