it both works in different way. it depends on what segmment you are targetting. for me, I would find Facebook more tangible and easier to create branding effect as it is not only text.
It is good question that Which is the best traffic source? Facebook or Twitter, I think both are most popular social book marking sites.but by the my idea Facebook is the best traffic source than comparison to Twitter.because it is more user friendly than twitter.In face book user are easy share his thought and ideas.
if both can give me equal traffic, I would be happy, however, it seems tht facebook works best for me. It's more tangible to me, stuff stucks thr for a long time, sometimes it goes lucky by appearing in other ppl's feed for 24 hours. however, twitter is more intangible, it's too real time to me.
I will say Facebook is better because of there simpleness. Actually the traffic is depend on uses and perfection of yours.