Need help deciding what to write!

Okay guys, I need a quick opinion.

I’m in the middle of a YA fantasy that I adore, but right now I have crazy inspiration for another book. I want to work on the new idea, but I’m afraid that it’ll keep me from writing book #1. I’m not really in the mood to write book #1, but I do really want to write right now.

What are your thoughts?

Thanks everyone!