Johnny Cash and Willie Nelson are both great.
One little thing, though, is that Willie's voice kind of gets irritating after...pretty much...the first song. He sings great, but the tonal quality limits are about 3 minutes. Then, I need to take a break.
I can listent to Johnny Cash much longer than that. Though, to be honest, I start feeling insecure about my manhood after about 30 minutes of listening to him. Wow, such a deep voice, what is wrong with ME?! Same when I listen to Russian men speak.
As far as what they have to say in their songs, I find Johnny Cash's songs much more interesting. They are either really fun (Boy Named Sue), socially aware, etc... Basically filled with deep passion. Willie's songs...welll...I don't really relate to "On the Road Again." "Old Yellow Line" (Which I heard sung by Dean Martin) can be interpreted as a metaphor for life, and "King of the Road" has very vivid imagery. But what goes on in "On the Road Again" is not really the experience of most people, none of the people I know, and I can't imagine a Vagabond's experience even being like that. "Always on my Mind" was sung a little to fast and hurried to be really "felt."
I'd have to go with Johnny Cash as being more "listen-able."
Willie is a great musician, though!