Now, if we could get the Unicode Consortium to add the graphical logo, I’d be sold. But if we must pick an existing character, I for one prefer the outlined star (⚝) much more than either the asterism (⁂) or the pentagram (⛧).
Unlike the pentagram, it aligns a lot better with inline text and looks nice and smooth. It’s also far less commonly used or overloaded with existing readings.
The asterism would be easier to unambiguously read or write by hand though! That’s its one pro.
Stars are perhaps even more common in written text for highlights and annotations than typed text, at least around here. I can draw a star much faster than three asterisks. But it wouldn’t be very easily distinguishable as the Fediverse star. And that’s the same between the regular sharp and pointy star and the rounded outline one.