Forgive me for disagreeing, PG--but I think it is easier to do a walking bass line in the A open position--
all you have to do is paste your index finger across the D, G, and B strings--
then hit the open A string,
then the same string with your ring finger on the fourth fret,
then hit the D string(which is already fretted at the second fret),
then hit it with the ring finger on the fourth fret,
then hit it with your pinky popped down on the fifth fret--