Now that's a very openly worded question. I could even answer "their logos" lol

Misskey's a vibrant colorful very interactive experience

Bluesky's a very good Twitter alternative, at least for now, although it's owned by a VC-funded startup so we'll see how long that lasts

Mastodon (and even moreso forks like Glitch and Hometown) are good if you want a small-to-medium size community along with the ability to be part of broader conversations. It can be a decent Twitter alternative for some people (especially white techies) but Bluesky's a lot more usable, easy to get started on, and diverse.

https://en.wikipedia.org/wiki/Fediverse