I switched from an HTC Incredible to the iPhone. For me, it was all about stability and ease of use. The Incredible was a nice phone hardware-wise. Where it stumbled was the Android OS. Android is a mess. I spent more time fiddling with settings and trying to find some kind of balance to preserve battery life than actually enjoying the phone. The final straw was when the UI started to crash intermittently when I received a phone call. There's nothing like having your phone ringing, but you can't answer it because the UI is busily rebooting (not the OS, but the HTC Sense UI).
As near as I can tell, the Android world has only worsened since I left it. Malware has gotten much worse, with malicious programs that record your identity disguised as apps. It's to the point now that most carriers recommend running anti-malware software on your phone.
The other place where Android falls flat is in apps. The worst iPhone apps are better than the best Android apps, period. And now that Android is so incredibly fragmented, trying to find an app that will run on your particular phone's feature set is becoming increasingly difficult. You end up running least-common-denominator Java apps that look like they were designed for a Commodore 64.
Then there's Android multitasking. Yes, it multitasks very well - but there's also no control over it. Most apps don't have "exit" buttons, so they just run all the time until your phone is turned off. With all of these apps consuming CPU cycles, the phone ends up getting warm in your pocket and depleting the battery like no one's business. The solution? Download a "Task Killer". Basically a little program that sits in the menu bar that you'll need to pull up constantly to kill off apps that you're done with. Well, most apps - some are embedded in the firmware (Skype and CityID were two of my least favorite ones). These will constantly auto-launch, and there's no way to stop them without "rooting" your phone.
I could go on, but I think you get the point. If you want something that works as it should, without a lot of drama, get the iPhone. If you link tinkering, tweaking and otherwise fighting with your computer, get an Android phone. It really does come down to just that.