The mods are largely just extra content (of varying levels of quality, honestly) added on to the base game, since it's not gonna get any more official updates. There's two that I know of, one isn't getting any more updates (kitteh0's version or something, I forget) and the other, xianxia, does still receive updates last I checked. Pretty sure xianxia also has most if not all of the other version's content in it, too, though I personally wouldn't recommend xianxia for your first time playing CoC.
Edit: After looking at the original game's thread, UEE (Kitteh6660's version) isn't getting updates, and HGG is all of UEE with extra stuff added, some of which is questionable content, judging from a google search and the original's thread. No idea if it's getting updates.