In an oversimplified way: when it comes to moderation, Lemmy is mostly like Reddit. The big difference is in the administration - each group of admins controls its own instance, with no group controlling the whole.

Where can I find a list of most active lemmy instances?

Here’s one. I’m linking this one because it allows you to look for communities (“subreddits”) too, not just instances, so it’s comfy to use.

If I want to make a community, is there a reason I would choose one lemmy over another?

Yes. For most of the time, it’s probably better to create the community in an instance focused on that topic, as people who like it will probably gather around that instance. So for example:

• programming stuff - programming.dev
• weaboo stuff - ani.social
• science stuff - mander.xyz
• furry stuff - pawb.social