Robert Hughes paints a slightly wordy but reasonably convincing case for Robert Rauschenberg as the best American artist of the 20th century, over in The Guardian. I think I probably agree with him, although Rauschenberg is certainly not the best artist of the 20th century overall. That honour belongs to Picasso, Dali or Bacon; I can’t decide which.
One thing I do recall from the last exhibit I saw of his (at the Guggenheim in New York, 1997) was his inordinate fondness for biros. Probably not what I was supposed to take away from it, but hey ho.