I think that Twitter is best for marketing & promotions but we could not dare to deny the fact that Facebook is best for social networking & community gathering. Facebook is more widely used in our region than Twitter because its applications are easy to handle & simple to understand.
For me both are good. I like facebook because of privacy and i like twitter because of it's following and retweeting option.
I use Facebook mainly for interactions with friends' wall, status updates and just looking around. I use Twitter to know exactly what is going on in and out the country. It's like an interactive newspaper, especially if you follow CNN etc. I love both but lately, I am more of a Twitter person (especially if you have twitter on your phone)
Facebook is #2 site in the world. I guess it's better rely on it in business. Twitter is gaining more and more popularity though... Why not combine both?