It has to be facebook.
- The maturity level is much higher (since it started off targetting university students).
- Its much more uniform in colour and layout (you know on each person's profile where each thing is*) unlike myspace where anything can be anywhere in any colour.
- Its far more modular meaning easier navigation.
- Photo tagging rocks!
* This has kind of been messed up by applications and the people who insist they have every possible application there is loaded into their profile.