Depends on your goals. Generally iOS is considered to be more a lucrative platform to develop apps for; iOS users are more likely to pay for apps. If you want to be an indie developer for profit, you should pursue iOS.
I personally prefer Android as a development platform. Android is more innovative, more flexible, arguably better designed, and more enjoyable for me to use. But that of course is just a preference. Try out a quick walk-through tutorial of iOS and see which you prefer.