Harry Truman. He had to make perhaps the most difficult decision of any president. Lincoln did not really make the decision to enter the Civil War, it was made by the events of the time. Washington was a first rate general and got the country off to a good start. Kennedy's mark must be 'incomplete'. FDR was the longest serving president and perhaps the most pragmatic.
Who would be the best choice for the next president? Oprah might be the top of the crop. I would follow her anywhere. Trump might be good. Hillary could probably do a good job. How bout George Clooney? No. I don't think Ameican would ever vote for an actor for President.