IOS and sometimes more profitable bussiness issue people tend to buy more applications but this trend and changing with Android because the number of users is more important. So I would say Android.
Both Android or iOS have their own advantages and disadvantages. Choosing right platform depends on the business model, the monetary, target audience and all these factors are important depending on the situation. If your primary revenue stream is advertisements, go for android and if it is app sales, go for iOS.
I think you have to launch them both. if you want to save some money, you can make a hybrid app for both platforms using html5, like Ionic framework. It would save you some money.