Google's Music Manager runs in the background on your computer; as your iTunes library changes, new songs are uploaded to Google Play, making them available to your Android smartphone. Playlists are also sycned, but not smart playlists or podcasts. That means music on Android gets close to the no-brainer it is in an all-Apple environment.
Video is another story. To get videos onto your Android smartphone, you can buy or rent them from the Google Play Store, downloading them to the device over Wi-Fi -- similar to how iTunes Store's video service for iOS, OS X, and Windows. But you can't sync the videos in your computer's iTunes video library to your Android device, as you can to an iOS device. The same limitation applies to photos.
Unless, of course, you get a third-party utility. Samsung offers the Kies utility on the Galaxy S III, and you can download the Mac or PC client from Samsung. It's sort of a poor man's iTunes, syncing music, videos, photos, and podcasts, as well as contacts across Kies-enabled devices. It can even import these items from an iPhone, iPad, or iPod Touch, as well as from any libraries on your computer. Kies works both over USB and via Wi-Fi (for Android devices that have the Kies client installed, such as the S III). Note that the Kies client did not work on OS X Mountain Lion until just last Thursday, when Samsung issued a compatibility update. Kies works OK, but it's clunky compared to iTunes.
A better and popular iTunes equivalent for Android is DoubleTwist, which comes in three parts: the free DoubleTwist Desktop for your PC or Mac, the free DoubleTwist Player for your Android smartphone, and -- if you want to be able to sync over Wi-Fi rather than just a USB cable as well as stream to an Apple TV -- either the $5 DoubleTwist AirSync utility or the $10 DoubleTwist Pro Player (an in-app purchase that also allows podcast syncing) for your Android smartphone. My only caution about DoubleTwist is that it tries to access your contacts, which it has no need for to do its job; OS X Mountain Lion automatically alerts you to this attempt and lets you block it.
To use the free DoubleTwist syncing, you need to connect your Android smartphone to your computer via a USB cable. If you have a Mac running OS X Mountain Lion, you can't do that -- USB syncing between Macs and Android devices doesn't work with OS X Mountain Lion. This is true even if you install Google's free Android File Transfer utility for OS X. (Windows needs no transfer app; it has built-in drivers for Android devices' storage access. But you still need an app like DoubleTwist to do more than see the Android device as a storage device.) DoubleTwist users can use the $5 AirSync add-on to get around this USB issue in OS X Mountain Lion.
For e-books, the only real option is to avoid Apple's iTunes' iBookstore and use the Amazon.com Kindle, Barnes & Noble Nook, or Google's Play Books services instead, as their readers are available for iOS and Android.
Apps: Content apps are easy, but productivity will sufferThe 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 is available for only the iPhone 4S and later on iOS. (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. 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.
AirPlay streaming, iMessage chat, FaceTime videocalling, and AirPrint: You lose these (well, almost)Apple has been pushing the use of zero-configuration network services aggressively in both iOS and OS X. In the OS X context, AirDrop allows for drag-and-drop file sharing among newer Macs.
But AirPlay and AirPrint are the two major services that people use based on Apple's Bomjour zero-configuration networking. With AirPlay, you can mirror your screen or stream audio to a stereo or TV connected to a $99 Apple TV device. With AirPrint, you can print over Wi-Fi to any AirPrint-enabled printer.
There's a huge seduction in what these services offer: being able to simply share music and videos from the device you happen to have in your hand. But you won't get so seduced in the Android platform, where each device maker deploys its own streaming functionality -- or chooses not to. When available, streaming is typically restricted to the vendor's own media devices.