Apps: Content apps are easy, but productivity will suffer
The iPhone didn't invent the mobile app, but it did reinvent it as a consumer-quality experience, rather than as a simplistic front end to some back-office system, the types of apps most common in the BlackBerry era. iOS developers have created hundreds of thousands of apps, several times as many as Android developers have. For several years, Android apps tended to be not only fewer in number but also later to the game and less sophisticated.
That's been changing, now that Android smartphones outsell iPhones by 2:1 or 3:1, depending on the market. If you bring an Android smartphone into the mix, you will have to repurchase the apps that have Android counterparts or functional equivalents to what you use in iOS. I found that the apps I used for content consumption and e-commerce on the iPhone were also available for Android, with mainly equivalent functionality and polish -- the Android experience has improved considerably.
For example, I have Android versions of the following apps that I use on my iPhone: Chrome, Dropbox, Flashlight, Google Voice, HootSuite, Quickoffice, SketchBook, and Skype for productivity and utilities; Allpoint, Amazon, AmEx, Concur Travel, Fidelity, Kayak, Pay by Square, RedLaser, Safeway, Urbanspoon, and U.S. Bank for banking and commerce; and BART (the regional subway system), BBC News, Caltrain (the regional train system), the Economist, IMDB, Kindle, Reuters News Pro, Soundfreaq Remote, TiVo, Twitter, and USA Today for information and entertainment. Android has a built-in navigation app with voice directions, which its iOS counterpart, Apple Maps, has only for the iPhone 4S and later. (The free Waze iOS app works better than Apple Maps and runs on any iPhone model. Waze is also available for Android, and I prefer it over the built-in Navigation app.)
What don't I have on Android that I have on iOS? Sophisticated office productivity apps such as GoodReader, Keynote, and Pages, and sophisticated media apps such as iMovie, iPhoto, Photoshop Touch, and Snapseed -- though Quickoffice is avaiable for Android, and it's among the best productivity suites in iOS as well. It remains true that the more desktop-class the app, the less likely it is to be on Android. But the truth is that I use the apps sparingly on my iPhone -- their use is largely for emergency touch-up. I typically work with them instead on the iPad, along with iPad-only apps such as Office2HD.
If you use an iPad for the "heavy" apps, Android's relative deficiency in this area is not that meaningful on your smartphone.