Dewey always came off to me as a very classy, authoritative fellow; He had, I think, perhaps not the cunning or intellect of FDR, but definitely the stately or statesmen-esque persona that made FDR so loved, whereas I've always looked at Truman as little more than a political hack--He was an OK president but had none of the insight, depth, intellect or even political mastery that FDR had.
That's funny, because I see it in an entirely different way. I see Truman actually as a man with greater backbone then FDR, and roughly equal intellect. By all accounts I've seen, or heard of, FDR has neither great backbone or intellect, but great temperament.