What fingering do you prefer for the basic left-hand shuffle / bass line?

• 5-1 & 5-1

• 5-2 & 5-1

I naturally started using 5-1 exclusively, but I notice that when the fingerings are written in, it says 5-2, 5-1. I'm still wondering if there's an advantage to either one.

Note: By basic shuffle / bass line I mean the bass pattern that alternates between the fifth and sixth. In C Major you'd play CG, CG then CA, CA.