Twitter hands down wins the the best social site award. Seems to interface better for business purposes. Example if I was selling something on Ebay, the second I tweet it, I have dozens of page views, product sells very quickly. Unlike when I use my Facebook account not so much traffic. My main grunt with Facebook is I have to keep switching from my personal page and my business page. If they intergrated the two than it would have much more purpose. Don't use MySpace ever. For traffic I prefer Stumbleupon.