I chose lemmy.ml based on two things:

• I wanted a server that wasn't likely to close I don't really know for sure, but I imagine it's easy to underestimate how much money or time is required to run a server. And I'd really prefer not having to worry about migrating. The 'run by Lemmy's developers' part makes me think that either the risk will be lower or the people running the server will know how to prevent reaching a point like that.
• I didn't want to join a very specific instance As I see it, there are two possible scenarios:
  • The instance I join will affect the content I'm exposed (and not exposed) to, in which case I want to experience 'the whole internet' rather than a section of it.
  • The instance I choose is irrelevant to the content I get, in which case, (apart from community rules) it shouldn't really matter which one I choose, so I would just join the biggest instance.

Still something that could help with the choosing-an-instance process is to display in the list of servers the community rules and if they are blocking certain communities.