Richard Nixon. He did much more for his country during his tenure then most on this list, and was exactly the kind of leader needed after LBJ. Shame about the Watergate thing.
I would agree that Nixon was a pretty good president aside from Watergate. As for me, I chose Reagan because he cut taxes (promoting economic growth) and helped end the Cold War peacefully. FDR's leadership during World War II was great, and, looking at it objectively, I would consider him our third-greatest president (behing Lincoln and Washington, respectively), but even many liberal historians acknowledge that the New Deal didn't end the Great Depression. Most believe World War II ended it, which I don't entirely agree with, but even one of my history professors said that the New Deal didn't get us out of the Depression, and she happens to be quite liberal.