Mostly #Wordpress, yeah, assuming they're not just hosting on the existing Webtoon/Tapas/ComicFury/etc infrastructure.

If you want something simple but customizable, give #ComicFury a try. (It's free, so if you don't stick with it, no loss.)

If you go with WP, get the #Toocheke plugin+theme combo. It's versatile, pretty easy to use, and actively being maintained.

Some creators also swear by #Grawlix. And #ComicControl is a new one in development that looks promising, but I'm not sure if it's available for beta testing yet.