I feel like the UI for Kbin is cleaner, though not without its problems. And I can access Lemmy communities from Kbin as well (this works a lot better than I expected it would), so I'm not really missing out if I choose it over Lemmy.

I'm also giving an answer to the other thread on Lemmy, since I think there are good reasons to use that one as well. They're both solid, and I'm using both regularly--often viewing posts from one service on the other. For me, it's "yes AND," not "no BUT."