Should I develop in IOS or Android?

You will have to decide exactly which type of smart phone user you want to target first if you don’t want to build both at the same time.
As they are two very different mobile platforms that require two very different types of language (Android apps are predominantly done in Java, while IOS ones are mostly done in Objective C or Swift) and native UI / UX design. For total market penetration you eventually want to develop for both IOS and Android. Rami Maki also builds for Windows, Blackberry and any other software or website platform.