What's your favorite social networking site, and why?

I, personally like Facebook the most…even if certain areas, such as photosharing, have been executed more efficiently on other sites, and are easier to use. So, which one is your favorite, and why? What sites have executed each area of networking the best? (For example, I think Facebook is the best in terms of updating you on what’s going on, and their message and comment system is the best in my opinion.) Or, do you even like social networking sites? Why or why not?