Worst
Andrew Jackson: Virulent hater of Native Americans. Launched a genocide program against them. (And it's not out of context to call it that, considering his language and intent.) Also killed the Bank of America, causing a series of panics over the next several presidencies. An iconoclastic, power-hungry dictator.
James Buchanan: Simply ineffectual, in all things, at all times.
Ulysses S Grant: A man of great personal integrity with no ability to judge others. He took away nothing but his salary from the Presidency, but many people enriched themselves in national scams they launched with Grant's support.
Warren G Harding: An utter cynic who appointed an incredibly corrupt cabinet. Its members not only stole the government blind, but maintained a whorehouse at public expense for their own visits and their friends.
Dwight Eisenhower: Always pushed off hard decisions on others, and left them flailing after they were made. His major debacles include a complete lack of comment upon Senator Joe McCarthy's Commuinst witchhunt, and his call for Eastern Europeans to rise against their Soviet masters--without lifting a hand to help them once they did revolt.
Richard M Nixon: Do I need to say a word?
Ronald Reagan: Numerous scandals during his administration. Economically bankrupted the nation. Began dismantling what little safety net existed for the poor (legal services, etc). Created enormous waste in spending. Foreign policies were a disaster--most notably, his support of Sadam Hussan, who was provided with chemical weapons. Domestic policies included the destruction of several vital wetlands, and the removal of laws limiting media monopolies.
Dubya: This one's pretty obvious.
