The best thing about AirPlay is that it just works. It takes about two taps to send audio from an iPhone to an Apple TV or other supported device. The downside to AirPlay is that Apple owns it exclusively, and accessory makers have to pay a licensing fee to use it in their products. That means customers pay more for an average AirPlay-capable speaker vs. a Bluetooth box.
DoubleTwist, a small developer team behind some gorgeous Mac and Android apps, has an open source alternative to AirPlay called MagicPlay.