I think the answer is different for each business. For SEOmoz, Twitter is our primary social channel. That's where people come to ask us questions, where we promote our posts, announce site outages, etc. Our customers use Facebook to communicate with us about 1/10 as much as they do Twitter regarding our site. I don't have the traffic stats in front of me, but I know for communicating with our customers, Twitter beats Facebook hands down.
And I know for other companies it is just the opposite. They'll have all kinds of conversations with their customers on Facebook, and nobody talks to their Twitter account. Try it out, see what works for you.