Additionally, there's the usability hurdle of interacting with non-home instances from outside mastodon. If I pull up someone's blog and click the little mastodon social media icon, it may very well link to mastodon.world. If my home instance is mastodon.social, now I have to launch into my own server, search up the account, and then begin interacting.

It's trivial to do but it is an extra step, but for your less-tech-literate friends and family it can be a point of confusion. Mastodon handles federation great in-ecosystem, but the broader web is still going to treat each instance as a different site.

As someone who’s not familiar with federated services, I don’t know what to base my instance decision on.

As I said elsewhere, many people just want a place they can go to share memes, news, opinions and misinformation. But on the other hand, there are plenty affiliated with interests/hobbies/identities/ideologies where you can to share topical memes, topical news, topical opinions, and misinformation (as long as it's on topic).

Snark aside, I'm on two instances: one for socializing, and another for my interest in cybersecurity. So I'd start with: do you want an experience that's more typical of social media with a more general pool of people, or do you want to focus on a specific interest but with the understanding that entails a smaller userbase and a slower feed?

If the latter sounds best to you, what communities do you find yourself most active in on other platforms (e.g. reddit, lemmy, facebook, twitter)? If not, we can find a relatively well-populated instance that's likely to have staying power.