If you go here you can sort by size, uptime, etc, I’m not sure if anyone has made a curated list anywhere. There’s only a few instances with 100+ users, but since you’re seeing all the same fediverse content anyway it doesn’t matter much. My policy was to just pick an instance I trusted (already trusted Blahaj, so that was easy).

I would say it’s probably a good idea to pick an instance with at least 30-40 people, because the more people who have subscribed to remote communities, the more content will will automatically federate to the instance (therefor making it easier for you to find new content).