Product Infra vs Web Fullstack

I'm an incoming Facebook 2019 Winter intern and am choosing the what part of the stack I want to focus on. I only have 1 internship under my belt and wanted to ask what y'all would recommend for someone with limited development experience. I'm still not very sure what I want to do in my career yet but also would really appreciate if you guys help me clearly distinguish between the two. Which would be more beneficial for an intern in terms of easier transition, more interesting work, better learning experience...etc? Selections include: android/ios fullstack, android/ios backend, web fullstack, product infra, and backend infra. Thanks!