I have the FB app for iOS, Android, and WP. I think they are all pretty bad or just mediocre at best.
The FB on iOS was better back in 2009. A better and easier to navigate layout. I hate the sidebar on the left. The Windows Phone is less cluttered to look out, but also very barren and doesn't update that much. And the Android is like the iOS version, but much worse. Keeps asking me to take a tour when I don't want to. I'd say iOS is the best followed by WP and then Android which is more of a poor man's version from the iOS' version. But they ALL need improvement. None are that good, but can still be useful. It is like the official Twitter app. Not my favorite or the best, but I can still use them esp on WP and Android.