No Way Down is good, no question. K2: Savage Mountain, Savage Summer is OK, too. Can't say which is better as I read the second one twenty years ago and can't recall a thing about it, except that it might be a bit 'in-crowdy', if you know what I mean. But the first one is real good.
More of a challenge is to find a book about K2 that ends well. Is there one?
In reply to Flinticus: Five Miles High by Bates and K2 Savage Mountain by Houston and Bates are classics, as is the book about Weissners expedition prior to WW2.
Buried in the Sky is excellent and a take on the last tragedy and should be read alongside No Way Down as well as Surviving K2 by Wilko Van Rooijen.
Currans book K2 Triumph and Tragedy covers the 1986 disaster and has a more informed narrative than The Endless Knot by Diemberger.