Both are very different, but I think Facebook gives more possibilities and it is not as stiff as twitter.
Facebook appeals to people looking to reconnect with old friends and family members or find new friends online; the mashup of features like email, instant messaging, image and video sharing, etc. feels familiar, while Twitter on the other hand encourages you grab ideals in byte-size chunks and use your updates as jumping off points to other places or just let others know what you’re up to at any given moment. Both are good in their own way.