Before he was assasinated Abe Lincoln was considered pretty much a bust as president. Not the worst, but definitely not a great leader that everyone thinks of him being today. Remember - under his watch, the Union split and the most deadly war in US history raged. Everyone expected the insurrectionist Southerners to be put down quickly but it turned into a 4 year blood bath. The conscription up North was hated and caused riots and violence.
And before people jump up and claim him the champion of freeing the slaves.... He didn't free the slaves. He set in motion the wheels to eventually free the slaves. His Emancipation Proclomation proclaimed the slaves in the South free in order to give the war a righteous cause. Though slaves in occupied areas were freed upon the proclomation, most slaves did not gain freedom. Lincloln wasn't president of the South of which the proclomation applied, so his words meant nothing in the Confederacy. He did not proclaim slaves in the border or northern states free. Freedom of all slaves was not officially granted until after his death with the 13th and 14th amendments.
The combination of the war finally being won by the North and his assasination is what gave Lincoln his legendary status. It can be argued that had he been a better leader, then slavery could have ended without bloodshed and the war avoided and seccesion avoided.
This just shows how you can list almost any president in the 'best of' list...or the 'worst of' list... depending on what you choose to look at during their tenure as leader of the country.