AirPlay is an Apple technology that sends sounds to Apple products (which are using iTunes) in a home through a Wi-Fi network. AirPlay is Apple's take on Bluetooth. Compared to bluetooth, AirPlay can be used to send music to multiple devices, and moreover, there is no loss of sound quality.

The best affordable AirPlay speaker: Wren V5AP (affordable and compact)
The second best AirPlay speaker: Libratone Zipp (you don't need a Wi-Fi connection to play music, 4-hour battery life, good looks)
The AirPlay speaker with best sound: JBL Authentics L8

Sonos vs Airplay: Although not AirPlay cpmpatible, Sonos speakers are simple to set up, have a solid wifi reception, and are compatible with all popular phones, tablets and computers except Windows Phone.Sonos Play:1 is the best-sounding Sonos speaker, according to experts.

Sonos devices also Play-Fi, a newer technology to access streaming sounds from DTS that works with iOS and Android devices as well as PCs.