Lincoln. He would have instituted a lenient Reconstruction plan, thus avoiding much of the bitterness which followed the war.
I agree. The dismal post-Civil War period is one of the most tragic missed opportunities in American history, in my opinion. We are still living with the effects of it to this day.
A less harsh reconstruction would have, in the long run, eased the transition of blacks in the south from slavery, and put the south on the path to recovery a lot sooner. The race issue would have been of much lesser importance had this taken place, rather than another 100 years of quasi-slavery for blacks.