Without sounding too "self serving," I want to suggest the edition of the
autobiography that I edited in 1990 under the title "Mark Twain's Own
Autobiography" (Univ. of Wisconsin Press).  There are genuine problems with
Paine's and DeVoto's and Neider's editions.  Most importantly is
that the three ignore Twain's own intentions for the autobiography.  My
edition -- as well as the version that is part of the Oxford Mark Twain
series -- is taken from the 25 installments that Twain chose and edited for
the North American Review for 1906 and 1907.  I make a case for
this version in the introduction that I wrote for Wisconsin and in the
afterword that I wrote for the Oxford Twain.

There are, in fact, over 2,500 pages of autobiography on file at Berkeley.
And given the range of editorial challenges in dealing with the manuscripts
and the dire state of humanities funding generally, I suspect that the Mark
Twain Project will not get to the autobiography while any
of us are alive.  What we might, then, explore is the version of the life
story that Twain left to us.  It's VERY different from Paine and DeVoto and
Neider, most importantly, in the image of family and emotional ties that
Twain had.

Anyway.  You might take a look.