The only thing close to a Mastodon reference index we have fell out of Forum Axe around a year ago, so let’s make something a little more lasting. Or maybe this should be merged with the friend code list in the era of platform redundancy? Maybe this thread should only exist in the Axe? Who knows.
I have little doubt, aside from factors related to timing, that you would want to be anywhere except witches.town but I have not yet joined mastodon myself (mostly because I often forget to sign up when france’s witching hour comes to pass)
That being said, I don’t think there’s any significant difference between mastodon instances aside from which other instances they block.
Ah, the other major differences are in moderation policies, but for the most part, the left-leaning social justice minded instances share the same moderation policies. Just be sure to read any rules/FAQs from instances you are interested in.