iPhones and Android smartphones are in fierce competition and both the platform are growing at a significant rate.
Where the Android market share is growing since 2013, Apple is still the undisputed king in the North American region.
So, before you pick any platform, you need to tally it out with your mobile app market.
We would recommend you to go for both the platforms if you are a growing business, willing to explore international territories in near future. If your business is local, you can check out the mobile platforms used in the nearby regions and accordingly pick the one.