I think both can be used to direct traffic to your website. They are both some of the world's largest social media marketing website
Personally when I've updated my blog or published a new ezine, I will publish those updates on twitter. If you have a large base of followers, this could really benefit you but that is not to say that a small group of followers won't either.
In the long run, you can maintain a steady stream of followers or even add more followers. Twitter is your microblogging platform and if you know the potential from blogging, never underestimate twitter.
You can also use Facebook to direct traffic through a few ways. One way is through their pay-per click adverts program, which works pretty much like Google Adwords but its cheaper. If you've blown a lot of money on google adwords try using facebook ads instead.
Creating Facebook groups can also direct traffic to your website. If your group happens to be interesting to a lot of people, it will spread throughout the whole network and you can pretty much imagine how it would work for your site. Facebook in short is viral in nature.
I hope this helps. You might want to read more from an article here. http://www.wordtracker.com/academy/social-media-ma...