Correct me if I'm wrong, since I've never used it, but Twitter seems like a stripped version of Facebook. It looks like it's just an aggregate of written statuses. I guess its one advantage over Facebook is that, since it's so stripped down, celebrities are more inclined to use it to post **** about their daily lives and possibly communicate with fans. Facebook can do the same thing, but I guess Twitter is more suitable for that purpose. Also, since there is such a focus on statuses, Twitter seems to be the more convenient platform for posting witticisms, especially given ease to retweet things.
But I have nothing interesting to say to the world, and I don't particularly care for famous people, so I stick with Facebook. It's almost necessary to keep up with the cultures and happenings back home and in college.