I like Facebook too much than after i comes to the twitter but still Facebook have rich facility like Apps and others.
Stumble upon is really good site for social media and for traffic and I am also using twitter and tumblr as social media.
I'd go with Digg and Delicious! Both of them are just fabulous! Digg brings in good amount of traffic than delicious, moreover the traffic via digg is genuine and interested in the niche of your website. So you would get the type of traffic you wish for.
I use facebook it's a very helpful for getting more traffic on site.It was launched on January 2004.Today, it has 901,000,000+ users.
I do used twitter, facebook and pinterest as my social networking and these are effective in driving traffics to my site and you can also use them by promoting your business.