I like the UI better, like that it interacts with things like Mastadon, and, what was honestly the biggest thing, doesn't have a dumb auto-refresh I can't disable (which Lemmy did (at least for a while)).

They both have a lot of growing up to do. Not being able to collapse threads in kbin is driving me crazy; especially for long threads with many nested levels, I can't tell what is even top-level.