Dunno, but you can take a look at instances.joinpeertube.org and sort by the metric you find most relevant

the-federation reports active users.

The only one I see linked often is tilvids.com. There may be more popular ones though.

Do you have an instance and/or channel to promote. I wanted to look into peer tube, but have not found anything intersting on the first look.

I like mp-tube.de it’s mostly German

Maybe https://sepiasearch.org/ is a good way to discover content on peertube. It’s a PeerTube search engine.