In the last couple of weeks, I’ve tested a few social networking related sites, such as: Facebook, Twitter, LinkedIn, Hi5, ILike, MySpace and a few more (beside Live Spaces which I already use since December 2004).
While some of them are oriented to specific types of networking (i.e. LinkedIn is more business oriented, Hi5 is more friend oriented), and therefore I cannot actually compare all on the same standards, in my opinion however the best one is Facebook: it includes several easy to use and Ajax-based features, including public fan-aware presentations on virtually everything, polls, quizes, and other applications, beside the standard wall of comments, notes, photos and friends.
I also like Twitter for sharing short status messages or links without changing my Messenger tag line. Facebook also can be set to receive Twitter updates as status text, which is great.