According a report being released by StatsCounter, Symbian OS is the top os of the year 2011.
After getting a lot of positive feed backs from its users for Symbian Belle, Symbian has won this crown. Symbian Started with 30% of market share this jan and finally ending with an improvement of 3.63%. The competitors other than Android got a down fall in their market share this year.
According to some other sources, the growth of Symbian is due to Nokia's decision of re-releasing Symbian under the license of open-source.