Some people think that in order to measure the influence of a tweep on Twitter, you should only look at the number of people following him/her and hence the larger it is, the more influence that tweep has. However, the number of followers is a misleading indicator of influence!
To actually measure the influence of anybody, you need to figure out how many people are listening to them(#followers), how often do they talk to their audience (#tweets), and how often they get mentioned by others(#RT’s).
Therefore, when deciding who to add to your account, make sure to check those parameters and not only the number of followers because while someone might have a lot of followers, he/she might not be active enough to capitalize on them.
You can also refer to the Klout score to find a measure of any tweets influence or you can check your impact by going here to the Twitalyzer website which has recently released the list of the most influential tweets and contrasted it with that of most followers.
5 Most-Influential People*
4. Stephen Fry