I probably fit into one of those two categories, I grew up in a religious family, but now don't know what I believe, or if there is something to believe in, agnostic/atheist is probably about right as to where I am from a spiritual perspective.
How this has affected my Sobriety? not in any way, I don't attend AA and didn't attend rehab, so the question of a higher power didn't come into play, the only question for me was am I going to drink today? no I am going to stay Sober until bedtime!! Great, job well done, move onto the next day and repeat.
Sobriety in my mind doesn't have to do with anything to do with faith, Sobriety is about not putting an alcoholic drink to my lips today, I keep it simple, don't drink and my life continues to look up!!