If you're trying to decide whether you should be writing fiction or biography/memior, I think there's a simple test you can do. Think back to something that has happened that you think could make a good story. Once you have the scene or event in your mind, see what questions pop into your head. Do you find yourself asking, 'What if ...', or do you wonder what happened next?
If you're a 'what if' writer, you will probably gravitate towards fiction, because you'll be somebody who uses every snatch of overhead conversation as a springboard for imagination. If you're an 'and then what' writer, you'll probably be an excellent researcher and will work really well in the field of biography, because everything you hear and learn will take you back to the source and your research to find out more.I think I am the latter - at least when I am writing for this blog.
[1] Lyall-Watson, K. (2013). Bringing the dead to life. WQ 234, p. 11.