I use Fediverse Explorer - click Active Users a couple times to sort decreasing. So the largest is Lemmy.World, bigger than the next five combined, and after that one they really drop off fast, with the rest being more alike in having merely hundreds or few thousands of active participants, rather than >18 thousand.

These “instances” (servers) make up the Fediverse, along with other federated platforms such as Mastodon (X/Twitter replacement), Friendica (Facebook replacement), Pixelfed (Instagram replacement iirc?), etc. Lemmy is software meant to replace Reddit, and then there’s a few unique ones that are related but have much fewer users: Mbin, which offers connection to both Mastodon and Lemmy software at once, and PieFed that is an entirely new thing, somewhat like Lemmy but not aiming to replace Reddit as the latter does and instead offer entirely new features (like democratization of moderation where users can control their own experiences, rather than have to depend upon a moderation team to tell them what they can or cannot have - I think it’s highly worthwhile going through it’s sign-up wizard just to see what it’s all about, even if you for sure plan to stay on your current instance, so that you’ll see it first-hand what is coming! other great features include categories of communities, basically multi-reddits, and hashtag support, neither of which Lemmy has). Both Mbin and PieFed though have fewer than 1k users total across all of their instances (shown in those links above), which is expected to change as they begin to be supported by apps - e.g someone is testing PieFed in a fork of Thunder right now.

But fwiw, Lemmy.ca looks to me like a fantastic instance, especially if you are located in Canada (for lower ping and increased relevance/interest to you), and it is the #6 top-ranked instance. So unless you prefered PieFed or Mbin software rather than Lemmy, it would make a great home. My only beef with it is that it federates with Lemmy.ml (for reasons not worth going into here:-), but this is exceedingly common among all of the top 20 instances (and most others as well), and you could spend a lot of time searching for “better” than Lemmy.ca without finding it.

One mantra for using Lemmy: block early, and block often - the people who were too toxic even for Reddit came here, and we have lost many people who expected the platform to curate their experience for them, yet we simply are not given the tools to do so: you need to do such things on your own. As you do, pay attention to which users submit content, what communities you are reading it in, and as you get more experienced, what instances are involved. They are NOT the same at all - they have entirely different sets of rules about what is allowed where.

But there are great discussions to be had here:-). Especially as Reddit gets more enshittified every day. You will probably like it here:-).

This isn’t comprehensive, but is a pretty good indicator of the largest servers.

Note that you don’t need to be using that instance to be able to read their content or post there.

Just to clarify, all the Lemmy servers you can join are interconnected as if they are just one big platform with the same content, so the experience is pretty much the same regardless of the server you join. The server you choose is just your door into the Lemmyverse.

Each server may have slightly different policies, but ultimately the goal is that you don’t have to think about it (other than knowing which server you are a part of so you can log in). However, it’s smart of you to consider how big a server is as some of the small servers might be more likely to shut down due to lack of maintainers or funding. That’s the main downside to the not-for-profit, decentralized nature of Lemmy/Fediverse—but so worth it in my opinion.