I think it's probably Dublin Blues because of the great lyric;

I have seen the David, seen the Mona Lisa too;
I have heard Doc Watson play Columbus Stockade Blues.

But then it might be Rita Ballou, because of the great laugh line:

Wild eyed and Mexican silvered, trickin' dumb old Cousin Willard
Into thinking that he's got her this time

On the other hand, it might well be Randall Knife:

If a better blade was ever made, it was surely forged in Hell.

It could also be Virginia's Real, just 'cause it's so much fun to sing and play on the guitar and watch people who don't know it fall further and further behind on the chord changes (sadistic s**t, ain't I?).

It could be LA Freeway Blues, which has such a great chorus to sing;

If I ever get offa this LA freeway, without getting killed or caught - expresses the way I always feel, driving on heavily trafficced urban freeways.

I'll think of more possibilities later, and probably post again.

Peter.