For me it's all Facebook, baby! More features, more application support, more "flexible" if you ask me and I didn't have but only a few (like 5) friends on MySpace, where as on Facebook I've got hundreds! 🙂
I also like the fact that Facebook has a "default" look for most parts. I seriously disliked MySpace's "auto-play musicplayers" and constantly changing views because of peoples' page modifications. It was always difficult to browse.
I also dislike that bands had "normal" profiles and for instance if I'd like a band and I've have friends, they'd all be listed in the same place? Doesn't this look stupid?
Mike Smith, James Ridge, Bob Marley, Brad Johnsson, Metallica, Janey Myers...
Seriously... They NEED to have a different place (in Facebook there are Friends, Groups and Pages listed in different places... I like that)
I also think Facebook has LESS commercials. The small boxes on the right don't even get my eye. I never actually even "see" them even by accident. On MySpace they're too "centered" for my taste. The bigger, the more annoying.
So all in all: More friends, more apps, more features, simplicity (design and looks), popularity and more... 🙂
Where I live MySpace isn't even that used... Don't know but a few people that use it, where as EVERYONE is on Facebook! 😀 Well atleast 90% of the people I know. The old and the young.