The iPhone has a very simplistic operating system with everything you need. It has a good app store and decent specs. It looks pretty and feels like a premium device. There's also iPod docking stations everywhere you go, so charging this device shouldn't be much of a problem. Having an iPhone is the in-thing. The in-crowd will think you're cool and they retain their value for longer should you eventually decide to sell it on eBay.
The iPhone is very restrictive. It's dependant on iTunes, you can't change the ringtones unless you practically hack the phone or pay out good money on iTunes, updates are known for being problematic, bluetooth doesn't work, it's extremely fragile, the battery can't be removed, the SIM tray is a pain to open and and it takes a mini SIM card that no other phone uses, though this can be fixed with a microSIM adaptor.
Using Android is like using a phone-sized version of Windows desktop. It's technical but simplistic and so open and friendly! You can even download a Sega Mega Drive emulator for free (with no in-game adverts) and download every single Mega Drive game (ROM) for free - and they run beautifully (this would never be allowed on the iPhone).The app store is just as good as Apple's, the Desire which runs Android has a removable back and battery, a microSD card slot and it takes a normal SIM card. Bluetooth works normally, the phone is tough, solid and rarely scratches and the specs are decent.
The only downsides with the Desire are its lack of 720p video recording, its poor internal memory (though this is compensated for with the SD card), no front facing camera and a battery life that's ever so slightly worse than the iPhone 4's. HTC technical support is also sub-standard compared to Apple's.