First of all, Iphone is a phone, Android is a mobile OS. Are we comparing IOS to Android? Or are we comparing phones, in which case which two phones, Android is used on a lot of phones.
I think the graphics on the iPhone is better.
Uh, that depends on the phone, not the OS.
iPhones are less open which makes it more secure. Androids are pretty open, but have security issues.
It also limits what a developer can do. Developers for android have access to so many of the phone's features that iphone doesn't allow. Any app you need to jailbreak an iphone to get, you can get an app that does the same thing (and more) without doing anything to your android.