I use Friendcaster. I like it more than Facebook for 2 reasons. 1) It loads WAY faster than facebook. 2) It saves your position in the News Feed, which I like because I prefer to start at the bottom and "read up" (oldest to newest), instead of starting at the top and "reading down" (newest to oldest).
With any 3rd party facebook app, you going to experience 1 (potentially) big problem. Under privacy settings on facebook, each user can set it so that 3rd party apps can't access their data. I think this was really created for facebook's web-apps (e.g. farmville, etc), but it applies to 3rd pary clients too. So if any of your friends have that privacy setting turned on, you won't be able to see any of their posts, comments, messages, etc.
I have a few close friends that have that privacy setting turned on, so I end up using a combination of Friendcaster (for general FB reading) and Facebook (to interact with specific people).