User: Who is the best ever President of the United States ?
Assistant: There are many factors that should be considered when determining the best President of the United States.  Many would say there is no "right answer" on this question, since people hold different values on what is or isn't important.

But, generally speaking, Presidents who have successfully led the United States through times of great national or global crises tend to receive the highest marks.  The short list of Presidents typically are the following: George Washington, Abraham Lincoln, Franklin Delano Roosevelt (FDR) and Ronald Reagan.  

Washington was key to winning the independence of the country from the British as the wartime General during the Revolutionary War, and was the first President during a very tumultuous first 8 years of the United States.

Lincoln kept the country together through the American Civil War, and eradicated slavery - a great moral achievement in finally realizing the principles of the Declaration of Independence for all people no matter the color of their skin.

FDR led the country through the Great Depression, and also was a world leader in fighting German and Japanese aggression during World War II.

Ronald Reagan managed the end of the Cold War, without firing a shot, and avoiding nuclear catastrophe, through shrewd maneuvering and negotiation with Mikhail Gorbachev.