Mobile web app vs. responsive web app

Hi, I am developing an app for mobile and tablet devices but not for desktop (my app use the device camera and photo library). What are the advantages and disadvantages of publishing it as a mobile vs. responsive web app? My aim here is to test and demo the application with users on different devices and screen sizes (mobile and tablets only) and to make the experience feel as native as possible (because that’s my final aim - to develop it as a native app).

On the one hand, the documentation on responsive web apps mention that " If your app in designed only to be run on phones, consider publishing as a Mobile Web App", but then the documentation on “Generate Screenshots” seems to imply that I wont be able to test different screen sizes with mobile web apps(?), but only responsive web apps. Is this the case, and what would you recommend?

Thanks for your help.