I've gone back and forth between iOS and Android phones for a while:
iPhone -> iPhone 3GS -> iPhone 4 -> Samsung Galaxy S2 -> iPhone 4S - Samsung Galaxy S3 - > iPhone 5 -> Nexus 4
I have both the iPhone 5 and Nexus 4 at the moment, but truth be told, as much as I like my iPhone, the Nexus brand might keep me on Android for the near future. I've posted my iPhone 5 on the local classifieds to see how much I could get for a sale.
At first the Nexus 4 battery life was kind of crappy, but once I got a custom kernel/rom on there, it's been within 95% as good as my iPhone 5, for my usage.
Another poster mentioned the camera, which is entirely understandable since the Nexus line has never really had a good camera, but for me it's usable. I take maybe 5% of my photos with my phone, most of the time I have my DSLR when I'm out taking pictures. For the quick snapshot, the Nexus' camera does just fine.
My opinion: If you're a techie, or like (want) to customize your phone more than just a wallpaper and folders, then right now an Android device might be the way to go. Of course, Apple could change things come the summer with iOS7, but then we'd just have to reassess our needs. Although with that said, for me, the only Android brand I will ever get in the future will only be the Nexus brand. I've always hated OEM custom UI skins no matter how much nicer they've gotten recently. Stock (or at least a ROM based on stock) Android is the way to go.