Personally, I went with Lemmy because it seems to be quite a bit further along in it's development. It also doesn't look like kbin's developer is recruiting much outside help, if you look at the repos of the two projects on GitHub/Codeberg, Lemmy has tons of contributions from people while kbin is mostly just the one guy with a few commits here and there. Not to mention that Lemmy's way less of a resource hog because it's written in Rust whereas kbin is implemented in PHP. Also, as far as I know federation is still currently broken on kbin.