I rate legacy in terms of something a president can call his accomplishment, i.e.:
Reagan—Total defeat of monolithic communism and winning of the Cold War.
Eisenhower—The Interstate Highway System, beginning of nuclear power, especially the nuclear Navy, school integration.
Kennedy—Space exploration, man to the moon, creation of Spec. Ops in armed forces.
Truman—Ending of WWII, dropping A-Bomb; integretion of Armed Forces.
Ford—Holding nation together after Watergate.
LBJ—Civil Rights legislation.
GHWB—Gulf War I (incomplete)
Clinton—Bosnia (overshadowed by failings on Somalia, failure to capture OBL).
GW Bush—9/11 aftermath but incomplete on Gulf War 2; (he will rise with stable Iraq and Afghanistan; stay where he’s at on my list if they aren’t stable because of Katrina, economy).
Nixon—Opened China, but overshadowed by Watergate.
Carter—Egypt and Israeli peace accord but seriously flawed by rise and humiliation of Irani capture of Americans, Desert rescue flop, economy, and Islamic fundamentalism fomented by Ayatollah Khomeni).
Kennedy's main achievement was giving inspiring speeches, like the "I am a jelly doughnut" speech at the Berlin Wall. The space program began under Eisenhower and the first moon landing was in the Nixon administration.
Abe Fortas was one of LBJ's Supreme Court picks, and the one who resigned under fire, after LBJ's attempt to elevate him to Chief Justice had failed. Nixon gave us 2 good justices and 2 terrible ones. Eisenhower gave us Earl Warren, which seemed like a good idea at the time but which he later regarded as one of his worst mistakes, I believe.
Truman's most important accomplishment was crafting a strategy for the Cold War--and he had a harder time than Eisenhower since he was dealing with Stalin, and Eisenhower was dealing with Stalin's successors. I don't know if Truman could have done anything to prevent mainland China from falling to Mao. He might have prevented the Korean War if he had not agreed to partition Korea in 1945, but that was an afterthought at the time, I think.