The primary reason to have an account with Lemmy, Kbin, or Mastodon as opposed to each other really just comes down to UI preference more than anything else. Which design feels the most clean to you. What special features have the devs built into the platform. That's really it. Though it's also worth mentioning that they're emulating different types of social media. Lemmy and Kbin are emulating the same type - the forum style we recognize from Reddit. Mastodon is emulating the Twitter "microblog" type of social media. Frendica is emulating Facebook. PeerTube is emulating video sharing services like YouTube and so on. So reading Mastodon data in Lemmy would be like trying to read tweets as Reddit threads. It doesn't transfer very well. As far as I've heard, Kbin is trying to create a better way of reading Mastodon style data within their platform. In the long term I'm willing to bet many of these platforms will implement similar cross-functionality for the different "versions" of social media.

For me it’s trust. Do I trust the hosts of lemmy.world to host my data? Do I trust they behave responsibly in their domain so that they one day aren’t blocked from other large instances? Can I invest my data in this instance and build my internet points within their service? What happens if all my points are lost because they get hacked or one day just close down? Gathering internet points is hard work and it has a lot of benefits. As you might have noticed, some people are considering selling their 10 year old Reddit accounts to spam bot farms. They will pay good money for a credible and old account.

Our world is changing. Having a job in the traditional way is just one way to create value. Picking the right instance might one day be like picking an employer. What values do you want to build? Who do you want to invest your time and energy into?