Among my peers where I've observed how they use FB, I think it's an even split. For me, if there's a web site, I skip installing the app. And of course a majority of news and social and commerce web sites now prompt you to install the app.
Personally when I occasionally use Facebook its via the app so that I am not logged in in by browser. Don't want them spying on everything I do online.
Twitter on the other hand I use in the browser as I like to be able to open threads in tabs to come back to.
