The first and most obvious difference between iPhone and Android is the plethora of devices available with Android. Multiple manufacturers means competition, which brings about innovation and choice. It also drives prices down. As a result there are far more Android phones out there to choose from.
Android is leading iOS becsuse Android overtook Apple’s iOS app store to lead in number of downloaded apps. Android users are now downloading more mobile programs than iPhone and iPad users combined. Probably 44% share vs. Apple’s 31%. This is despite the Android Market only having 319,161 apps at the end of last month vs. the Apple App Store’s 459,589.