There are two kinds of people who claim that Mastodon is the best.

One, absolute fanbois and fangurls who, in addition, don't even know that Pleroma, Misskey or any forks of either exist, much less what they're like. Their point is always "biggest = most popular = best", although they themselves, like almost everyone on Mastodon, were railroaded onto Mastodon without being told that there's more to the Fediverse than Mastodon, even in terms of microblogging.

I'm not even kidding when I say the UX on the *keys is closer to Twitter than that on Mastodon. And at the same tiime, the *keys show what Fediverse projects something comes from whereas Mastodon tries hard to make everyone believe that the Fediverse is Mastodon.

Two, Mastodon devs. I've actually had a Mastodon developer who knew that I'm on Hubzilla comment into my face that Mastodon is literally the only feature-complete Fediverse project. I could have inquired him about Mastodon support for one or two dozen Hubzilla features, ranging from full HTML rendering over nomadic identity and WebDAV/CalDAV/CardDAV connectivity to a built-in wiki engine. But I didn't.