Blogs and Facebook are two different things so you can't really pick just one.
I use facebook if I want a more targeted communique. The single best thing with facebook is the tagging feature. I can tag anyone that I am friends with on my status updates and uploaded photos. If their friends see the photos we made I get instant recognition. And if those friends comment or like the photos their friends (the ones I don't have access to) get to see my work and so on. It's very viral and very fast.
I use blogs as my personal
PR machine. It's one-directional and geared towards
SEO. You can't show up on searches with facebook alone so you still need a blog. Also, who knows if facebook goes down at least you still have a way to communicate with your clients.