Actually, two of those are, in my opinion, the LEAST honorable politicians of the 20th Century. I am, of course, talking about the Kennedy's, arguably THE least honorable men to serve in Washington. Not only did JFK have absolutely NO moral standards (whether good or bad), but he was a horrible President as well. His brother, was no better, although he, obviously, was never President.
To further narrow the field, I meant Americans, as this entire thread is about America. That leaves us with Truman, Stevenson, Eisenhower, and King. I don't like Truman. He fired MacArthur, my favorite military officer of American history (I don't care whether it was warranted or not. In the end, MacArthur will be proved right). Stevenson was, although a nice man, a little too "red" for my liking. He was a good person, but he would have ruined this country had he been President. Eisenhower was a politician, pure and simple. He was a master politician and administrator and a relative do-nothing as President.
As for King, the last man on your list, I have only a tiny inkling of respect for him. He was made of the same moral fiber as the Kennedy's. You're talking about a man who slept with white prostitutes and plagarized his doctoral thesis. His constant criticizing of the US government's foreign policy, especially during the Vietnam War, really got on my nerves. The best thing about King: the day off from work.
There you go. Out of the Americans on that list, it is my opinion that Barry Goldwater is the most honorable.