You can't beat the range of apps on the iPhone. I've been disappointed with the apps on my Android phone - still no Sim City!
Also the iPhone integrates very nicely with iTunes, making it very simple to operate and transfer media.
However it does lack some things - you can't just use it as a USB flash drive - whereas you can with Android. The memory is built-in, most Android phones use MicroSD (which you can plug into an Micro-SD to SD adaptor, and thus into an SD-USB adaptor) which is handy.
You can often get Android phones on cheaper tariffs, but on an equivalent tariff I would get an iPhone 4 these days.
