sorting by "popular" in the modpacks section of the twitch client, the most popular ones at this time are RLCraft and Skyfactory 3 & 4.
obviously RLCraft is hell on earth,, but i don't know about the Skyfactory series of packs. the 4th one is for version 1.12.2 and has 2.4 million
downloads so i'd say it's pretty popular.
on curseforge it says 3.1 million downloads for Skyfactory, so i'm not entirely sure how accurate the figure is, but here it is: