When I tell (write) stories, I visualize myself sitting with my ancient ancestors around the fire (that we just recently tamed). I tell stories about my experiences, stories about other people’s experiences, and stories about the gods, the forces of nature, and mythic heroes. The first of these I tell in first person point-of-view. The other two are in third person. For me, the root of the story determines the narrative voice.
My current project is told as a memoir and thus is first person. I am telling the true story about how I was accidentally taken to an alien world and ultimately saved Earth from annihilation. (If you wonder why the world did not end on 2012-12-21, it is because I saved it.)
My next project will be told in third person. That story tells the tale of a group of heroes who go beyond what I did. Those heroes save the Universe.
How do you see the story you are writing? Is a character telling us their personal account about what they did and experienced? Or, are you, as the storyteller, telling us a story about what someone else did?