@jgilbert for your question, depends on what they're here for. If the goal is subscriber numbers and statistics, mastoson.social will do, but instagram or bluesky are more adapted.

If you're here for genuine noncommercial contacts with lovely people, any instance will do even the generic ones, as soon as it's normally federated.

Mastodon.art is quite strict regarding moderation and general instance quality, but most others are not that rigorous.