both os are based on user preferences. Android has a lot of customisation. iOS has better hardware management. In terms of security,it looks like android is more vulnerable but since almost 90-95 percentage of mobile users are using android, more testing and an attempt to find a vulnerability is done by developer or hacker community so that large number of people will be affected due to this. In case of iOS it doesn't have a large user base as compared to Android, so it is not so attractive for hacker community