Lemmy.world initially cause I didn't like the overbearing moderation and locked communities of beehaw.org and the developers of lemmy.ml. Kbin seems to be great and I prefer its timeline / sorting, I just wish it was a bit more polished with magazine syncing and certain UI features, but that should come with time.
I've created accounts on all of those and kbin is by far my favorite. Lemmy.world has some sorting issue where all the "hot" posts are two days old. And the others are just overzealous in their moderation or push weird political takes on non-political communities and I'm not really fond of that.