I think, for me, if it's a band I know almost anything about and enjoy beyond 1-2 of their big hits, then I prefer a documentary.
I really didn't like Bohemian Rhapsody (as a movie, performances were good) because I really love Queen and know a decent amount about them.
I really didn't like The Dirt because it was a god awful movie. But a good Motley Crue biopic would have been fine since I don't care about them beyond a few of their greatest hits.
Same with Elton John. Looking forward to Rocket Man (which may suck) because I just know his big big hits and very little else.