It depends on your intentions: if you're trying to find the merely most popular thing, it's still twitter. But you'll have a much harder time being noticed by groups that twitter has been modified recently to disfavor. As a result, mastodon and bluesky have grown somewhat; bluesky has the advantage over mastodon that it's very fast and scalable, and as such my impression at the moment is that it's growing faster. But it's definitely still an underdog. If you want to talk directly to people, find the people you want to talk to on whatever platform they're on and talk directly to them. But if you want to talk to groups, I'd say there's not one town square, but one per platform. And bluesky being mainly progressive folks means that if you want to talk to progressive folks, it's a much better place to go than twitter right now.

The reason I used the phrasing "if you want a strong connection to public opinion you can't skip" is because I expect twitter is obvious and a given, but the strong difference in cultures is causing enough people to not stay on twitter that only using twitter means you're missing people based on their opinions on divisive topics.