I absolutely adore Youtube and all of its features. (Well. Maybe not the new layout and the horrid implementations that they wish to put in place in future). There's such a large variety of things to see. Music, movies, animation, comedy, horror, everything! (well maybe not EVERYTHING, but you get what I mean
). Youtube has so many possibilities that facebook lacks. I'm not even sure if you can really compare the two. Facebook has its benefits as a social networking site, but fails as a video sharing site. Youtube fails as a social network, but excels as being a video sharing site for the exchange of ideas and thoughts on various topics.
However, as an overall site, i'd prefer youtube. Facebook is too connected with my real life, which I don't particularly like. Youtube is a whole new dimension which has barely any ties to the real world, or, at least, my world, which is why I enjoy it so much.