In my role and with my company, we staff both an iOS and Android team. I can tell you from experience that it is harder to obtain good Android mobile engineers than iOS. It seems that more developers gravitate to iOS than Android. That being said, past trends use to have companies focused more on iOS than Android, thus I can understand why previously engineers focused more on iOS. Trends are changing and have been. Currently for any new native mobile App effort we start, unless there is a very specific reason why, we run both an iOS engineering team and Android team.
I agree with the previous response in that more important than anything else is making sure you have a firm, solid, and deep understanding of software engineering. This will include software constructs, algorithms, and design patterns; they will transfer to all languages.
The short answer to your question that I will provide is this, learn both. If you can present yourself as a native mobile engineer familiar with both platforms and able to write code, review code, and design, that will by far separate you apart from most others. If you are considering "picking a side" to start with, I would start with Android. I feel trends right now show more of a need for Android engineerings than iOS. But, I would strongly consider how you can integrate learning both.