I use both Mastodon and BlueSky and I don't really care for platforms like Twitter. Both Mastodon and BlueSky are good in their own ways but I think BlueSky is user friendly. Easy to setup looks super similar to Twitter, easier to navigate.
Plus, I have heard about it pretty much everywhere. It is commonly compared to Threads. I only know and heard about Mastodon on Lemmy.
As someone who uses both. I think Mastodon also just doesn't have the users, it is not as easy to setup and I think understanding instances and its UI are less user friendly.