Cats and Dogs is the best selling expansion pack

Another article:

The Sims 4 launched more than three years ago, but it’s still attracting new players. In Electronic Arts’s report for its third quarter ending on December 31, it revealed that the player base for the game has grown more than 35 percent year-over-year. EA also said that its newest expansion, Cats & Dogs, is also the best-performing pack ever for the game.

https://venturebeat.com/2018/01/30/the-sims-4s-cats-dogs-is-2014-games-most-popular-expansion/amp/?__twitter_impression=true