Oh man, do i really have to choose one here? I am a HUGE fan of all three. There is nothing better that socializing with a bunch of people I haven't seen for 15 years.
Myspace was a huge success because it was the first. It had and still has so many flaws that will make it fail without major change.
Friendster - appeals to Asians I believe because it's made for Asians.
Facebook - Built for Harvard students, then college students in general, then it changed it's image to full scale. It dominated the market because it was mostly made up of college students and not a ton of spam at the time.
Every socialing website will fail over time until one emerges that is amazing at reading the market and what people want in a socialing website, but that's hard because the internet is still young.
Never heard of tagged. Probably don't want to either. Facebook is good enough for me right now.
None. I had Facebook for awhile. Then I realized why I lost touch with these people - I couldn't fucking stand 'em to begin with. Anyone I want to talk to now has my phone number and can call me. I don't need a site to reconnect me with people I never really liked to begin with.
i've never heard of tagged but i am pretty addicted to twitter, and i've met alot of really cool people on there too. the cool people i've met on twitter are now facebook friends and conversations have different layers between the two sites.