A probably too long post about an entirely different way of viewing things:
I have accounts at... I guess about eight instances. I didn't see any reason to pick one, so I just signed up for everything that looked interesting and promising.
I expected to eventually settle on one, but as it turns out, I actually like having multiple accounts. I have four that I rotate between at the moment. Oh, and with the same username on each, though I still haven't decided if that's a good idea or not.
First, I have a kbin account and multiple lemmy accounts. Even though lemmy has more users, I much prefer kbin just as far as the software goes - it's just a better UI. And Ernest is awesome.
Beyond that though, each instance is a different experience, since the federated communities on each one are different, depending on what other instances they're federated with and which communities from which instances people have subscribed to. And I've amplified that by having different sets of subscriptions on different instances.
Kbin.social has a good mix of content but without most of the botfarm instances. I like that. That's where I do virtually all of my serious posting.
Lemmy.world (when it's up) has a wide range of content, but too much of it, even not counting the bots, is too shallow IMO. It feels too much like Reddit for my tastes. It is the best one to check in on for the most popular topics though, and it's where I'm most likely to be subscribed to communities for memes, humor, drama, pictures - all that sort of junk.
Lemmy.one actually feels like what it is - an instance that demands that users behave themselves. It's nice when I want to just unwind, because it's already the case that problematic instances are defederated, and I have a limited set of feel good subs there. I almost never post from there though, since I don't trust myself to behave.
Lemmy.ninja is my favorite. It's just quirky little instance with terrific admins and an amusing aesthetic. It's little though - 120 users last I heard. That shows in its all, which is fairly limited, presumably just because few people means few subscriptions so few federated communities. That's fine though - it's a selection that matches my interests fairly well. And ninjas are cool.
And I'm still on the lookout for a serious, scholarly sort of instance - somewhere that will be a comfortable home for subs to philosophy communities and the like.