Kbin is nice. It’s easy to register on kbin.social so might as well check it out, although they are possibly under DDOS attack right now. I’m on there and lemmy at the moment.
Both systems are very similar and are compatible. You can follow lemmy from kbin and vice versa. Lemmy is probably more mature, but kbin is also pretty slick and seems to be moving fast. The community on kbin.social is fairly large so you will likely find more interaction on there without having to subscribe to federated servers. That probably makes onboarding a little easier for reddit refugees. They also have a microblog feature that works like Mastodon (federated twitter alternative) so you get to use lemmy-like and mastodon-like in one app and federate with both.
The fact that kbin is written in PHP shouldn’t put anybody off. Modern PHP isn’t the same as the old stuff that earned a bad reputation. I haven’t used PHP for a long time, but my understanding is it’s now a solid stack that’s on par with other mainstream stacks.
Something along these lines seems more realistic to me. There will always be a place for easy, safe walled garden experiences with a low barrier to entry. In the fediverse, that could be a very large, curated instance where a broad group could find what they want without having to figure out how to subscribe to federated communities. Similar to how so many people were introduced to the internet via Prodigy, Compuserve, AOL, etc.