The Facebook app is fine, and I'm a fairly heavy user.
Many of the iOS and Android people insist it isn't good enough because it doesn't include features to manage groups, but I don't manage any groups so I don't care.
The other nice thing about it is that it doesn't include the spam from the iOS and Android versions. On my S3, whenever you log in to FB via the "official" app, half of your feed is "Joe likes Citibank. Sally likes Bacardi. Angelo likes American Airlines. Sam likes Samsung." None of that on the WP app.