Dylan was far clearer in diction in the earlier half of his career...and the accompanying music was much less likely to make the words harder to hear at that time also.

One singer who runs her words together and barely seems to bother to pronounce most of the consonants is Stevie Nicks. "Uhh....what was that you said, Stevie???" Other than that, though, she's a fine singer.

Now, getting back to singers with quavery voices that tend to slip off-key.....how about Neil Young! Yessiree, old Neil is the "King of the Quaverers" as far as I can see. ;-) Still he's quite good in his own strange way, so why should we complain?