Chael's was by far the best MMA fighter's autobio/memoir I've read. Funny, intelligent, well-written. Chuck's was enjoyable, too. BJ's was forgettable. I read both of Saku's autobios and liked them very much.
A Fighter's Heart by Sam Sheridan was written by a professional, so it was pretty good, but it focused a lot on sports I care for considerably less than MMA, so it wasn't my favorite. If you love boxing and/or Muay Thai in addition to MMA, it could be worth your while to read it.
Got to get around to GSP's one of these days.