No question in my mind-- the true purist is A, the person who tries to do it JUST the way it was done before. The best quick example I can give is Dixie, which the Skillet Lickers recorded (CO 15158, also on Document DOCD 8056). Now EVERYBODY knows the words to Dixie, right? Well, Riley had a momentary lapse on one of the choruses and sings "I wish I was in Dixie, hooray, hooray. . . (momentary pause) I wish I was in Dixie, away down South in Dixie, away, away. . ." When I get together with certain friends, we sing it the way Riley did, just as a point of pride to say that we are trying to get as close as possible to the original Skillet Licker sound. We have also been known to do DaCosta Woltz songs without a guitar, 'cause that's the way they did them.
Note that this does not address the question "which sounds better?" But very often we have found that deliberately limiting oneself to the techniques and sounds available in 1927 is actually liberating and definitely leads the player to a better understanding of the music. This really IS a YMMV.
   By the way, when we're doing Carter Family songs, our band usually uses TWO guitars, and autoharp melody techniques developed within the last 30 years. Authentic? definitely NOT, but also more pleasing to the modern listener.