The greatest United States president  

I think it is Bill Clinton. He has effectively handled the country & monica at the same time at oval. I think no american president has this distinction.

I would say either F.D.R. or John Kennedy. I'm thinking more on the lines of how successful and popular they were during the time of their presidency and even today. Roosevelt for example kept our country running well during WWII and got us through most of the war as best as he could. Especially considering the hardships that he himself must have been going through at the time and that he was disabled. He didn't let that effect his job as president.

by far from what i have read and i believe kennedy was the best and there shall never in my lifetime be a better one as he was !

no one really..

Ronald Reagan to us from double digit inflation, drastically lowered taxes which then spurred the economy to new heights,
oversaw the dissolution of the USSR.

We are still enjoying the benefits of his economic policies despite the best efforts of both Bushes and Clinton to undermine them.

Iran saw the light just after Reagan took office and released the hostages they had taken.

He had a no nonsense approach when dealing with foreign policy, and is rumored that he once told the Russians "The bombing begins in 5 minutes" when talks had reached an impasse.

So I would say Reagan