Ask HN: Is it better building an app or a website for an mvp?

I am developing my own startup and thinking about the next step I am wondering whether develop an Android app or a website. Is a social platform where users can interact. I have knowledge in Android so I could develop the app, and HTML&CSS but not enough to create the website.

The question is, what will be more efficient, to create the app, or learn more about lets say PHP and create the web, or maybe use a CMS as Elgg to create it