Firstly, why jump ship?
I had been using the iPhone 5 from Softbank for almost two years, and after successive iOS updates, the specs were no longer up to scratch.
I've never been an Apple fanboy, but to give credit where credit is due, the iPhone served me pretty well, performing simple tasks and lookin' good all the while. Despite the bugginess, iOS 8.1 is a complete and polished system, and beyond the crawling speed my old iPhone gave me, it was a mostly positive experience.
Simply put, I wanted to try something new.
With each successive Android release (currently 4.4 KitKat, 5.0 Lollipop coming soon) the touch and feel of the system improves dramatically. The vast majority of key iOS apps are also available on Android, so the day-to-day social media, mailing, reading, listening and watching is all covered.
What has really impressed me so far is the ability to customize your system down to the nuts and bolts. Don't like the UI/Launcher? Pick another one. Want to increase storage? Just pop in a larger miniSD card. Even the keyboard can be switched, not just the keymap.
In short, you can customize nearly every aspect of the operating system, and if you like even the OS itself (via warranty-voiding ROMs.)
One more feature that appeals to me is the inter-app operations that iOS often restricts. See a photo you like and want to share it? iOS might let you share it via a handful of key apps, Facebook, Twitter and Mail, but Android will let you hand-off the photo to any number of apps.
The one thing I've missed most is iCloud. The ability to sync your key information between your Apple devices is pretty convenient, for better or for worse. In particular, universal settings for calendars and mail accounts allows you to seamlessly keep up to date with work or whatever you need on the move. In addition, as of iOS 8 Apple introduced a number of new features, such as iCloud Storage to rival Dropbox and Google Drive, FaceTime integration with Yosemite and fingerprint recognition on iPhone 5 Plus and 6/6 Plus for maximum security.
With Android you can use Google's impressive array of apps for anything you need. However, migrating from iOS means finding a way to import your data or leave it behind. Contacts can be uploaded via Gmail, music libraries can be synced online if you're in supported countries, and social media apps take care of your account information themselves. Sharing data between devices just doesn't feel as smooth or flexible, especially after you're used to the slickness of iTunes. It feels like there's an extra step to most things you need to do on Android.
Things to improve?
If Android wants to increase its user share (especially in the Apple-dominated US and Japan), it needs to provide a smooth and fully-featured transition from iOS to attract current iPhone users. Another similar case is the Ubuntu distribution of Linux, which has made it trivial to migrate from proprietary operating systems like Windows and Mac OSX by offering like-for-like services behind a glossy UI. Android is some way there already, and the progress is encouraging, but not everyone will be dropping their iDevices just yet.