I read the Sanborn book when it came out, and felt the same
way that most people in this group did.  An alternative that I
can wholeheartedly recommend is Nigey Lennon's The Sagebrush
Bohemian, which was also published in 1990.  It concerns itself
with Twain's years in the West, and it is great fun to read.
Lennon prides herself on actually liking Twain!  The book
contains some of the same "revelations" about Twain's private
life that were in the Sanborn title.