I am using both of them in marketing my products and services. But I never post direct links, they drive people away. It's like they are allergic to those links. Anyway, going back to the comparison, paddy12 is right about the PR. Hence, using both would be more beneficial to your business.
As we know even the two are social networking site , Facebook are most commonly used by people because it is easy to used and people can directly connect to their friends and family unlike twitter.
Both seems looking good in my point of it. I personally prefer facebook because it is friendly users and big networking. Feel easy for business guys to promote it.
The data confirm that why Facebook or twitter is so well-known. They both have their different pictures like in Facebook or twitter you can create enormous fan system and reveal your pursuits and enhance your websites too, whereas Tweets is micro-blogging services and you have to go by individuals to create a enormous system over there.
Facebook are twitter both are the best for seo purpose but for networking purpose facebook is the best than twitter because we can fully use facebook for networking/communicate each other by sharing though and also chatting but we can't use twitter fulfill for communicate.