These polls come out about every year, and they change a little. Harry Truman seems to keep moving up, while Bill Clinton and Ronald Reagan have slipped a little. And sometimes, time removed from the office seems to affect the person's position. George W. currently ranks below Herbert Hoover. While I certainly don't think W. was a great president, I have a feeling history will be a little kinder to him (maybe lower middle of the pack).
Right after Nixon resigned, he was ranked extremely low. Then through the years, he moved up some (he was a good foreign policy president). Now he is slipping again.
I wonder how much current political bias plays into these historians' views?
I personally like the Teddy Roosevelt-Harry Truman-Lyndon Johnson type presidents -- who make decisions, and then let the chips fall as they might. We saw some of that in Reagan, too.
So who is YOUR favorite?
By the way: I heard Michael Irvin talking about this on his radio show yesterday. His all time favorite president? Barrack Obama. Yes, sir -- they guy has been in office for 1 month, and he already ranks as the greatest president ever? I hope history proves that to be true -- but come on!