I prefer Tim Buckley's original Song to the Siren to This Mortal Coil's version. I'm only using this as an example because other than All Along the Watchtower (I'd rather hear Bob sing it), it is the only example I have and the latter is pretty weak. Song To The Siren is one of my favorite songs of all time, and although Tim's version lacks the vocal tricks that Fraser is so great at, Tim's voice is so unique and pained yet beautiful. Plus he wrote it, so it feels more raw of course.
I agree and prefer the Cash version myself. It's his voice... so tremulous and haunting, that does it for me. When he sings these lyrics, I believe him; he is so compelling I have no choice. It's no stretch of the imagination to see him having lived and felt these words.
Is it heretical to say I usually don't like listening to live albums at home? Don't get me wrong... I love to go to live shows and listen to the artist's uncut versions of the album songs. It's especially entertaining when they throw in a little twist, something just a bit different from what you would hear in the studio. For example, I am a big fan of a Canadian Latin guitarist called Oscar Lopez. Went to see him and his Irish friend serve up a unique mashup of styles they affectionately dubbed "Celtino." :D It was a small, intimate theater in the artsy part of the city, and that only added to the vibe as Oscar tuned his guitar to produce wonderfully jazzy, off key renditions of his songs that raised goosebumps on my arms. He also broke a couple of guitar strings. Unfortunately, I don't get quite the same pleasure listening to most (not all) live music at home.
They used to say "you have a face for radio," which was a way of saying you sound better than you look. The advent of the music video changed all this, and put more of a focus on an artists' looks. I have noticed that the stars who became famous before the 1980s are often excellent live. They had to be. I don't think that's so much a case for today. Producers have an important job!