Don't ask the general population about a President's effectiveness or legacy; most can only remember as far back as their own lifetime. There are, however, rankings of the "best" or "most effective" presidents of all time by government institutions, news agencies and colleges that consistently rank Abraham Lincoln as #1, 2, or 3. The others that rank highly are George Washington, FDR, Jefferson, Teddy Roosevelt, Harry Truman, Woodrow Wilson, and Andrew Jackson. With the exception of Jefferson, all are somehow linked with being IN a war or helping the nation through a war. Lincoln's war happened to be the one where EVERYONE killed was an American (not true in WWI or WWII, but a "civil" war by definition is you against yourself -- no wonder it was the bloodiest of our wars) It was also a war, ostensibly about slavery but other issues were at play too, that had been delayed by weaker presidents leading up to Lincoln. Nobody wanted to free the slaves or divide the Union at the risk of his own political career, beginning with Jefferson's capitulation on a clause in his original draft of the Declaration, and an issue that was sidestepped again in 1810 and 1839 and then by every weak president leading to Lincoln -- Fillmore, Pierce, and Buchanan.
Make no mistake. Lincoln was and still is one of our greatest presidents ever and none of our most recent presidents come anywhere close to him. In the top 7, the most recent is Harry Truman who took over after FDR's death and had the courage to drop the bomb on Japan and the magnanimity to offer billions of dollars to help re-build post-war Europe.