Here is a list and search for all Lemmy commhnities, even ones your home instance is defederated from.

As for one instance being better than another, it depends on what you value. Size, sign-up procedures, moderation, and what instancea they’re federated with are all factors. As an example, Beehaw.org is a larger instance with some popular communities, but they have a strict sign-up process and defederate from a lot of instances. This gives their users a more curated experience, but some people don’t like having someone else controlling what they can and can’t see