Can't contribute much to the discussion here because I usually study battles and campaigns.
But I
have read three biographies on Grant, all of them very informative--and sometimes conflicting.
--Ronald C. White's
American Ulysses. This one has been mentioned a few times and remains my favorite (for now, anyway).
--
Grant And Sherman: The Friendship That Won the Civil War. Actually
two biographies in one! It doesn't delve deep into either subject, but still has some interesting facts that I never knew before.
--
Ulysses S. Grant: A Victor, Not A Butcher by Edward H. Bonekemper III. A nice insight into Grant's military genius, but don't read if you can't stand the bias (a problem for me). When he gets to the 1864 campaigns, Bonekemper takes time to drag Lee through the ashes. It's a good book, but I don't think it's great because his bias comes across as unfair.
Or maybe it's my southern upbringing. Who knows?