I've read so many that it's no wonder that I wrote a novel that reads like one (my novel Bad Movies). What movie star biography have you read, and did you like it? Did you believe it? Did you find it interesting?
One of the biggest problem with biographies is so many of the people writing them say sensational things they couldn't possibly know anything about, just to make the book fun fun fun. And gossip is often presented as fact.
One of the biggest problems with autobiographies is the star doesn't lie so much as commit the sin of omission - making it all a bit dull.
And then there's the Diana Ross/Faye Dunaway autobiography style, mostly just spending too much time trying to explain away old criticisms.