One of the main differences between Twitter and blogging is the number of characters that will be used by people who are trying to get their message across. Some people would only need to use Twitter when they want to rant about something or share something short yet sweet. Some people need to blog more because they believe that they have a lot of things to say.
They want to make sure that people will hear what they need to say. Some are good in writing while some just need to get the attention of people. It would be up to you to choose which one is more ideal.