Both operating systems are great.
The only difference between them is that Android is open than the iOS, this means you can do pretty much what do you want with your Android device. You can root it and customize as you wish, change kernels, overclock, upgrade/downgrade anytime and alot more. One more thing is that Android it's much more animated, but in rest that's pretty much it.
The iOS dosen't allow any of these it's pretty much a locked system. The only thing you can do it's "jailbreak" as far as I know.
The iPhones are have the best bulid quality, the apps are reviewed by the Apple before posting them into the App store, the design it's nice and classy etc. Another thing to say about iOS is that it's the most optimized system out yet. There is a good connection between the software and hardware since both things are made by Apple, while Android smartphones are made by
a huge number of companies, practically impossible to make it flawless on every single phone.
In short words:
iPhone = Classy, speedy, easy to use.
Android = Developers heaven, fits best for a guy who only plays a few games while at dentist or just texting up and down.