Hi,
I reckon any answer you get will be peoples preferences. For example, I would go for Android!
What I suggest is do research on both and post your findings and your choice in your report, listing Pros and Cons for both OSes. Think about the ease of development, as well as maintainability and portability. If you make one for the iPhone, you're restricted to that and iPad. With Android, you can cover more devices, but may mean more time and money (in the real world at least). Also, how do sale projections look based on current trends? If Android is going to be 5 times bigger than iPhone (iOS) in 5 years then will that affect your decision.
Overall, the end decision should be yours. And you should be credited for your reasoning.