Finally, a mobile Facebook client that I really like! Filpboard doesn't count, since it's not a real FB client, only displaying the news feed. Ah, which one? you ask. I'll tell you. The absolute winner is the Win phone FB app!
On my Android devices and on my iPad, 99% off the times when I open Facebook (which is several times in a day), I use the web page instead of the mobile app. With the Lumia, I was already so disappointed by the mobile apps - plus, Win phone has the People news feed, combining FB and Twitter feeds - that I didn't even think to install the actual WP7 Facebook app.
Until today, when I couldn't access my FB messages any other way, the full web page not functioning properly on the phone for some reason. And it was love at first sight. There is something to be said about the metro UI of the WP7 apps. It simply rocks!
The iPad version is more or less ok too, at least an unquestionable second place.