There are many programs to use Twitter, being Tweetdeck one of the most popular on Adobe Air, and Hootsuite one of the leaders in web environment.
Not all of them have the same functions or the same objectives, only some have thought of companies that have a group of people managing the same Twitter account, and they are the ones who indicate on dailybloggr.com:
With statistics and content management for groups, it is one of the most comprehensive options for this purpose.
It allows to program tweets, create campaigns and measure the effect of the included texts. It has no free option.
The king. With the possibility of importing RSS news, scheduling texts for the future, managing information in a group … it just lacks a good statistics module.
Excellent for those who care more about the reports of the campaigns created. A very good tool to analyze data and prepare new marketing strategies.
Very easy to use, with basic statistical modules, ideal for those who only need to write and answer together with their co-workers.
The one that was my favorite for a long time, with a very intuitive environment and with the possibility of analyzing keywords to plan strategies.