Since I'm in the midst of deciding what to do with the iPhone 4S and Nexus 4 I have, this is a very relevant thread for me.
I've yet to decide to stick with Android over iOS, and the more i use both, the more I strongly suspect I'll keep both. However, I realize that I've been using iOS in its various incarnations for over half a decade, and I've been using Android (not counting the Kindle skin) for a few months, and Android on the phone for two days, so there's a strong chance I might change my mind - either way - once I get more familiar with the OS.
If we exclude the mobile component, I generally prefer Android. I do find that iOS apps are generally more polished, and I appreciate that, but I also find that Play is so much nicer to use than iTunes/App Store. I like being able to find apps while browsing on any computer and have them sent to any device I choose. I like the variety of apps for rooted devices that are in one place (Play) instead of needing to go to an entirely different store (Cydia) on a jailbroken iOS device. I like that rooting happens almost immediately instead of potentially taking months (or forever) on a new iOS release. I like that, when I got the Nexus 4, it took pretty much zero time to have the "desktop" I'd set up on my Nexus 7 appear on the 4. Apps, of course, took longer, but the general look and feel were almost instantaneous, and that's over fairly crappy cellular at the mall.
If we include the design of the devices that run the OSs, then I'm still swayed to the Android side. I love the apparently endless battery life of the iPhone 5 (unlike the horrid battery life of my 4s) as well as that of the iPad line. However, I'm sick of aluminum. I love the look. I hate the feel. I prefer the feel of the 4S to that of the 5, but I prefer the feel of the Nexus 4 to that of the 4S. Why? No sharp, cold aluminum. Aluminum's great, but not when I'm holding it.
Ah, but now we come the the OSs when used in mobile devices as mobile devices, and in that case, at least as far as I can tell, iOS wins. Siri, as much of a fussy bitch that she can be, is better at stuff I want to do when I can't see the screen while driving than Google Play is (sending texts, etc.). The phone/contacts integration seems better. iMessage rocks. Generally, it just seems to me to be easier to make/take calls (including selecting the recipient) and to send/read messages.
So... I've got a decision to make, with one of the options being to use both. When not communication with someone, I prefer Android (JB 4.2 in particular). When communicating, I prefer iOS. My mobile devices alternate between both use cases consistently, so it's not an easy call (pun not intended).