Dylan - by a country mile, Dylan.
There have been some great names mentioned, so far - and some that haven't (Paul Brady, Tom Waits, John Prine, Mary Gauthier, Todd Snider etc etc) but Bob is something else again.
Like a Rolling Stone, alone has had two books written about it.
His lyrics are on the curriculum of more than a dozen countries' second level schools and have been accepted a third level since Oxford was the first to do so in the early 80's.
I'm not sure any other lyricist can match that recognition by the academic establishment.