This OR That

Help me.

I’m at a standstill. I’m trying to make the impossible decision as to which book to begin writing first. 

A sci-fi/YF book, or a book based on a certain 3 years of my life where I faked being a completely different person. 

I know which ever book I do decide to publish first it’ll likely tie me to that one particular genre and I don’t want to be known as that ‘so and so’ author. 

Suggestions/comments/concerns are welcomed.