It's FREE. And from the intellij source code. Designed by Google. I love intellij's line of product's new features and constant updating of it's IDE. It's like a kitchen sink of awesome tools. Add Google's constant support and development of it, and it becomes the ultimate android IDE. The new Android Studio update and Kotlin support is evidence of what I'm talking about. I have recommended Android Studio to everyone since the beginning.
A few years ago, Android Studio's default emulator was really slow and a pain in the butt to work with. And everyone basically had to use Genymotion's emulator. But it has since been updated and is as fast, if not faster than any of the 3rd party emulator software out there.
Did I say it's FREE? Unlike intellij's other software which cost a ton, Android Studio is provided by Google for free. FREE!
It'll really bog your computer down. You should have at least 4GB of Ram on a good computer to run android studio at the same time at it's emulator. Smoothly. I recommend going up to 8GB of RAM. I personally bought a 12 GB RAM laptop just so I can have multiple android studio windows and emulators open so I can work on multiple projects at the same time.
Look up TheNewBoston's youtube video on Android Studio interface. It teaches you the UI really quickly. Because if you have never touched IntelliJ software before, the whole kitchen sink of a user interface will confuse you real quick.
Building Android apps. Let's be honest here, what else are you going to build Android apps with? Eclipse? Eclipse is so buggy and outdated, it's not even a competition.