Well, Dylan's not had a good album since Waits started recording, IMO, so I'd have to go with Waits just for that reason. 60's Dylan = brilliant, but his post mid-70s output is fairly fucking awful. A fate he shares with plenty of his fellow travellers from the 60s, mind you. Look at Neil Young and Johnny Cash, some of the stuff they did in the 80s were beyond shit, although they did pick up again in latter years, Cash especially so.
As to the authenticity argument - in my experience this is a rhetorical device employed to dismiss artists that you don't like pure and simple (and nothing wrong with disregarding music based on simple likes and dislikes) in a way that sounds intellectually mature. YMMV.
I think Waits is much more aware of, or possibly plays up his characters, his role-playing a lot more than Dylan ever did. The fact that a good few of Waits' albums (The Black Rider, Alice, Franks Wild Years, Blood Money) have been composed for the theatrical stage probably strenghtens this supposition.