From SEO point of view, both are very important. You need twitter for updates and facebook for also for updates from your site. It brings in traffic to your site. GoodLuck, Rizecorp.
I disagree with most. FB is more like family oriented. Twitter is more business centric I think. FB can give a lot of traffic may be. But they will hardly become customers. From ROI perspective, twitter is better for business in my opinion.
I believe facebook is better, as i have learnt from many marketers that a lot of twittering (if that is a real word) leads to very few good results. You get a much greater return on your efforts with facebook.