There’s no general answer, it depends on your personal preference.

If you want to have most content available, register on an instance which has an according policy; which federates with anybody and is federated by everybody (both directions can make a difference).

The downside however is, this also opens the door to all sorts of bad actors, including bots and spam.

So I personally tried to strike a balance and am so far quite happy on lemm.ee.

This tool is pretty handy to make informed decisions: https://fba.ryona.agency/ It allows you to check federation status both ways.

There should be a place to document all the nuance around hosting an instance plus some tips and tricks.

The Wiki: https://joinfediverse.wiki/What_is_Lemmy%3F

Hopefully it gets new contributors and maintainers from all the new users.