That's a really difficult call for me at this point. I'm inclined to say 2017 for a few reasons. For myself, that's when Vampires released and it's my favorite pack of all time, it was exactly what I wanted. It was the first time in Sims 4's release that we had a lot of fun with some of the devs on the forums, over in the GP section and they were interacting with us and answering questions and the hype was real. I was cheerleading it myself, lol. But even generally speaking, 2017 was the year that toddlers released for the family players and they also got Parenthood, which is a widely praised pack as well, and Toddler's Stuff. So even though those family packs aren't my personal cup of tea, I do acknowledge that the release of more family play caused a big shift in the sub-genre of players who needed it, and the forums in general especially became a happier place. So it was a good year for family and Occult players alike.
But I've got to say, speaking as a vocal member of #TeamSupernatural, 2019 is giving 2017 a run for its money. Others may have been disappointed in this year's releases, but I'm over here celebrating the Year of the Occult/Fantasy/Sci-Fi Invasion. StrangerVille, Mermaids and Spellcasters are all released/releasing this year and I'm extremely pleased. It's been a long wait for some hearty, satisfying Supernatural play since Vampires. Yes, there were some minor Supernatural/Fantasy beings along the way, (plus Aliens if you like Sci-Fi) but nothing that had gameplay longevity what with Ghosts behaving just like normal Sims, PlantSims and Skeletons being buffs, and then little weird teaser tidbits like Patchy. As much as I appreciated these things, they just didn't fill in the gaps of a full life state. But this year isn't even over and there are rumors of University coming in the Fall, so we'll see where 2019 leads us and how the next packs play out.