I tried both, and I prefer the look of kbin, but ultimately I went with Lemmy because I couldn’t get kbin federation working. It’s only a matter of time until kbins improves, when I first tried Lemmy it was really tough to install from source on bare metal so I went with lotide instead. Unfortunately, Lemmy’s federation broke with lotide and kbin doesn’t federate at all yet so I needed something in a hurry that works.

Another thing that could affect my choice would be the back-end. With the backend of kbin being php and the backend of Lemmy being rust, I expect that if you’re hardware constrained federation could be more responsive on Lemmy. I experienced something similar when I moved from friendica (pure php) to pleroma (Erlang).

If it’s not a question of setting up an instance, I’d prefer kbin, and later on I might set up an instance once it’s had some time to mature.