If you want to make money, make iOS apps. It doesn't matter that there are more Android phones out there, people simply buy more apps on the iOS platform. Apple did a good job of promoting the app store and encouraging users to spend money there, whereas Google did fuck all like they always do with everything because they suck at being human.
You can do cross platform dev with tools like Phonegap or Appcelerator Titanium but you'll never get a 100% experience with them.
Also, iOS is objective-c, not c#. C# is on windows. Android is Java.