Interesting discussion! I would say that both are quite equal. However Twitter requires much more effort and time to do well for your business.
Facebook is really good for attracting end-users from all over the world, various contests, engaging your customers and visitors to do something creative that will help you spread the news about your business, as well as presenting your creativity and 'human side' of your business which is very important nowadays.
On the other side, I think that Twitter is more business targeted and there is a less place for a chit-chats and easy-going conversations with your clients and visitors. Twitter is great tool for making connections between companies and business oriented users, and above all, sharing your offer in a short and professional way to a range of receivers who are potentially interested with your message. Everything is rather straightforward and really concrete which is a huge pros in most of circumstances.
Imho, both are important and worth using, and they sort of complement each other.