They are both bad for different reasons.

Kbin has uncontrolled spam because the administrator, Ernest, likes to go AWOL for months on end and wants to do everything completely by himself. Currently, Kbin.social has been unreachable for 4-5 days - whether that's because something legitimately broke or Ernest pulled the plug on things we don't know because he actually hates communicating with people. He could gain so much more goodwill from the community if he just left a one sentence post saying "I am still alive, I am still updating things, be patient."

Lemmy World sucks because the admins suck, the moderators suck, and the majority of the userbase don't seem to be interested in creating quality content. Most of the people there are only there because their Reddit app doesn't work anymore.