You probably should not use number of users or amount of content as the deciding factor (that leads to centralization, remember the entire point of federation is to DE-centralize), that said…

The instance list does allow sorting by number of users or number of videos, phijkchu.com has the most users and Videovortex has the most videos.

Wow, you made me think! P.S.: I’m still new here on the Fediverse.

I think a better way to decide on an instance is reliability.

What is the instance, where is it based, who runs it. I don’t mean to completely dox people but they should provide some meaningful background info to legitimate themselves.

Personally I wouldn’t trust instances run by individuals unless I knew the people personally and I could talk to them. Otherwise you will always run the risk of leaving your content in the hands of someone who may or may not want to continue running their instance.

Is it run by a single individual, a group or an organization? I’d rather trust a group or organization and the more info they gave about themselves and their team and messaging the better. A group or organization is less likely to fall apart if any one person decides to quit.

A well organized group who know how to raise and maintain funds will also be less likely to fail.

And the user themselves have to make themselves responsible as well. Once you find a reliable instance that you like … give them money, support them, donate to them. The whole system needs money to operate and the people who make it work should be paid for their time and effort. If we all paid a little for every little bit of the fediverse we use, the more reliable and stable it will all become. The little bit we pay to every little instance we use will mean that it will be less likely to devolve back into a monolithic centralized corporation that controls everything all over again.